High-throughput non-invasive prenatal testing for fetal RHD genotype

Evidence-based recommendations on high-throughput non-invasive prenatal testing (NIPT) for fetal RHD genotype.

# Recommendations
High-throughput noninvasive prenatal testing (NIPT) for fetal RHD genotype is recommended as a cost-effective option to guide antenatal prophylaxis with antiD immunoglobulin, provided that the overall cost of testing is 24 or less. This will help reduce unnecessary use of a blood product in pregnant women, and conserve supplies by only using antiD immunoglobulin for those who need it.
Cost savings associated with high-throughput NIPT for fetal RHD genotype are sensitive to the unit cost of the test, additional pathway costs and implementation costs. Trusts adopting NIPT should collect and monitor the costs and resource use associated with implementing testing to ensure that cost savings are achieved (see section 6.1).# Clinical need and practice

# The problem addressed
NICE technology appraisal guidance on routine antenatal anti-D prophylaxis for women who are rhesus D negative recommends antiD immunoglobulin for all rhesusD (D) negative pregnant women who are not known to be sensitised to the D antigen, to reduce the risk of sensitisation. The British Committee for Standards in Haematology (BCSH) guideline on anti-D immunoglobulin to prevent haemolytic disease of the fetus and newborn also recommends that all Dnegative pregnant women who are not known to be sensitised to D antigen have antiD immunoglobulin after:
potentially sensitising events
birth, if the baby is confirmed to be D positive by cord blood typing.
AntiD immunoglobulin is produced from the pooled plasma donated by large numbers of Dnegative people who have had a transfusion of Dpositive red cells to stimulate the production of D antibodies. It is a finite resource and, because there have been shortages in the past, it needs to be used carefully to maintain stocks. AntiD immunoglobulin is a blood product and may also carry the risks common to all blood products, including physiological reactions, processing errors and the potential future risk of unknown blood-borne viruses or prion diseases. Physiological reactions must be reported to the Medicines and Healthcare products Regulatory Agency and processing errors to the Serious Hazards of Transfusion Scheme.
High-throughput noninvasive prenatal testing (NIPT) for fetal RHD genotype involves analysing cell-free fetal DNA in maternal blood and is intended for use in pregnant women who are D negative and are not sensitised to D antigen. It is a laboratory-developed test offered by the International Blood Group Reference Laboratory, Bristol. This laboratory is an accredited NHS Blood and Transplant Laboratory that is currently providing NIPT for RHD genotype for some NHS patients.
High-throughput NIPT for fetal RHD genotype would allow Dnegative women who are carrying a Dnegative fetus to avoid unnecessary treatment with antiD immunoglobulin.
High-throughput NIPT for fetal RHD genotype would allow Dnegative women to make an informed choice about whether to have treatment with antiD immunoglobulin. This may improve adherence to antiD immunoglobulin treatment, reduce the number of sensitisations and so reduce haemolytic disease of the fetus and newborn in later pregnancies.

# The condition
During pregnancy, small amounts of fetal blood can enter the maternal circulation (an event called fetomaternal haemorrhage). The presence of fetal Dpositive cells in the maternal circulation, after fetomaternal haemorrhage, can cause a mother who is D negative to produce antibodies against the D antigen on the fetal blood cells (antiD)  a process called sensitisation. Sensitisation can happen at any time during pregnancy, but is most common during the third trimester and delivery. It can follow events in pregnancy known to be associated with fetomaternal haemorrhage, such as medical interventions, terminations, late miscarriages, antepartum haemorrhage and abdominal trauma. These are called potentially sensitising events.
The process of sensitisation has no adverse health effects for the mother and usually does not affect the pregnancy during which it occurs. However, if the mother is exposed to the D antigen from a Dpositive fetus during a later pregnancy, the immune response is quicker and much greater. The antiD produced by the mother can cross the placenta and cause haemolytic disease of the fetus and newborn. This can cause severe fetal anaemia, leading to fetal heart failure, fluid retention and swelling (hydrops), and intrauterine death.
The risk of sensitisation can be reduced if Dnegative pregnant women have antiD immunoglobulin. Before antiD immunoglobulin was available, the incidence of sensitisation in Dnegative women after the birth of 2 Dpositive babies was about 16%. Haemolytic disease of the fetus and newborn, which occurred in about 1% of all births, was a significant cause of morbidity and mortality. After routine postpartum antiD prophylaxis was introduced, the incidence of D sensitisation dropped to about 2%. The sensitisation rate has further reduced since the introduction of routine antenatal antiD prophylaxis.
In England, there were 646,904 births from April 2013 to March 2014, of which about 15% (97,036 births) were to Dnegative women. About 40% of these women carry a Dnegative fetus (around 39,000 per year) and so do not need to have antiD immunoglobulin. Dnegative status occurs in about 15% of people of white European family origin, about 3% to 5% of people of black African family origin, and is very rare in people of eastern Asian origin. Most Dnegative people of white European family origin have an RHD gene deletion; less than 1% have RHD gene variants. However, in Dnegative people of black African family origin, 66% have an inactive RHD gene (the RHD pseudogene), which mostly results from genes that contain D sequences but do not produce D antigen.

# The diagnostic and care pathways

## Care for Dnegative pregnant women who are not sensitised to D antigen
In current practice, babies born to women who are D negative and not sensitised to D antigen have their Rh blood group determined after birth, using cord blood typing. Testing to find out the RHD genotype of the fetus during pregnancy is not currently done in most centres in the NHS.
The NICE guideline on antenatal care and the BCSH guideline on blood grouping and antibody testing in pregnancy recommend that women should be offered testing for ABO and Rh blood group in early pregnancy. All women identified as Dnegative would be tested for the presence of D antibodies, regardless of whether they are known to be sensitised or not. To prevent sensitisation in women identified as Dnegative but without D antibodies, antiD immunoglobulin is recommended, both as prophylaxis and after potentially sensitising events.
The NICE technology appraisal guidance on routine antenatal anti-D prophylaxis for women who are rhesus D negative recommends routine antenatal antiD prophylaxis (RAADP) as a treatment option for all pregnant women who are D negative and who are not known to be sensitised to the D antigen. RAADP can be given as 2 doses at weeks 28 and 34 of pregnancy, or as a single dose between 28 and 30 weeks.
The guideline from the BCSH on using anti-D immunoglobulin for the prevention of haemolytic disease of the fetus and newborn recommends that all Dnegative pregnant women, who are not known to be sensitised to D antigen, have antiD immunoglobulin after:
potentially sensitising events
birth, if the baby is confirmed to be D positive by cord blood typing.The BCSH guideline also states that RAADP should be given regardless of, and in addition to, any anti-D immunoglobulin that may have been given for a potentially sensitising event.

## Care for Dnegative pregnant women who are sensitised to D antigen
The Royal College of Obstetricians and Gynaecologists' (RCOG) guidance on managing women with red cell antibodies during pregnancy recommends that all women who are D negative and are sensitised to D antigen should:
attend pre-pregnancy counselling with a clinician who has knowledge and expertise in managing this condition
have their blood group and antibody status determined at the booking appointment (ideally by 10 weeks of gestation) and at 28 weeks of gestation
be offered noninvasive fetal RHD genotyping using maternal blood if maternal antiD is present.The NIPT offered to D-negative women who are sensitised to D antigen is different to the high-throughput NIPT for fetal RHD genotype assessed in this diagnostics guidance, and has different diagnostic accuracy.
The RCOG guideline and the BCSH guideline on blood grouping and antibody testing in pregnancy also recommend that if a Dpositive fetus is identified, additional monitoring and treatment are needed during the pregnancy, which should include:
measuring Dantibody levels every 4 weeks up to 28 weeks of gestation and then every 2 weeks until delivery
referral to a fetal medicine specialist if Dantibody levels are rising or are at a level above a specific threshold, or ultrasound features suggest fetal anaemia
weekly monitoring by ultrasound if Dantibody levels rise above a specific threshold
fetal blood sampling if ultrasound shows signs of fetal anaemia, and considering intrauterine transfusion
considering early delivery of the baby, depending on antibody levels and whether any fetal therapy has been needed
using continuous electronic fetal heart monitoring during labour.
After the baby is born, the RCOG guideline recommends that assessments should include:
a direct antiglobulin test to detect maternal antibodies adhering to the baby's red blood cells
confirmation of the baby's blood group (using a cord blood sample)
haemoglobin level measurement to test for anaemia
bilirubin level measurement to test for jaundice
clinical assessment of the baby's neurobehavioural state and observations for jaundice and anaemia.
The NICE guideline on jaundice in newborn babies under 28 days gives recommendations on diagnosing and treating jaundice.# The diagnostic tests
The assessment compared 1 intervention test with 1 comparator test.

# The intervention
High-throughput noninvasive prenatal testing (NIPT) for fetal RHD genotype is a laboratory developed test offered by the International Blood Group Reference Laboratory, Bristol (NHS Blood and Transplant). The test uses a real-time quantitative polymerase chain reaction (PCR) method for identifying fetal RHD genotype from fetal DNA in the plasma of rhesusD (D) negative women. The test analyses cell-free fetal DNA, in the form of small fragments of fetal extracellular DNA shed from the placenta and circulating freely in the maternal plasma. The level of cell-free fetal DNA in maternal blood increases throughout the pregnancy and rapidly falls after delivery. Most women who are D negative do not have copies of the RHD gene; therefore, the presence of the RHD gene in a Dnegative pregnant woman suggests a Dpositive fetus.
High-throughput NIPT is carried out using 4 ml to 6 ml of maternal anti-coagulated blood. DNA extraction is done using an automated robotic platform (MDx BioRobot, Qiagen), which can rapidly process samples. The robotic platform is also used as a liquid handler to dispense samples and reagents. PCR is then done on an ABI Prism 7900HT analyser (Applied Biosystems). Primers and probes for exons 5 and 7 of the RHD gene are used, and the following controls are tested alongside the samples: RHD positive DNA; RHD negative DNA; RHD pseudogene positive DNA; and no DNA. The samples can be tested in batches of between 32 and 88 samples. The time to complete the test from sample receipt to report generation is 5 to 6 hours.
The exon 5 assay amplifies the RHD gene, whereas the exon 7 assay amplifies both the RHD gene and the RHD pseudogene. A threshold value of less than 42 cycles is interpreted as a positive signal and an algorithm is used to determine the fetal RHD genotype. Results are reported as 'Dpositive', 'Dnegative' or 'indeterminate  treat as Dpositive'. The result would influence whether to offer routine antenatal antiD prophylaxis and antiD immunoglobulin to Dnegative women, who are not sensitised to D antigen, after potentially sensitising events.

# The comparator
The comparator in the assessment was cord blood typing, which is used to determine the Rh blood group of a baby after birth.# Evidence
The diagnostics advisory committee (section 8) considered evidence on high-throughput noninvasive prenatal testing (NIPT) for fetal RHD genotype from several sources (section 9). Full details of all the evidence are in the committee papers.

# Clinical effectiveness

## Assessment of test accuracy
Eight studies reported the diagnostic accuracy of high-throughput NIPT for fetal RHD genotype, all of which were prospective studies carried out in European countries. Four studies were done in England, 3 of which were based in Bristol. Cord blood typing was the reference standard in all studies. Six studies were considered to be at low risk of bias and 2 studies (Akolekar et al. 2011; Thurik et al. 2015) were judged to be at high risk of bias. Except for 2 studies (Akolekar et al. 2001; Wikman et al. 2012), the results of the studies were considered broadly applicable to using high-throughput NIPT for fetal RHD genotype for nationwide testing in the UK.
It is expected that, in the UK, women with inconclusive NIPT results will be treated as having a positive test with no further testing. Data on inconclusive results were not reported in 2 studies (Thurik et al. 2015; Grande et al. 2013). So, 4 approaches to the diagnostic accuracy analysis were considered:
women with inconclusive tests were treated as test positive (including Thurik et al. 2015 and Grande et al. 2013)
women with inconclusive tests were treated as test positive (excluding Thurik et al. 2015 and Grande et al. 2013)
excluding all women with inconclusive test results
including only studies done in Bristol.
Results of the hierarchical bivariate meta-analyses are shown in table 1. In all analyses, women in whom NIPT was carried out at or before 11 weeks' gestation were excluded because the test is known to be less accurate before 11 weeks. NIPT for fetal RHD genotype is very accurate among women with a rhesusD (D) positive fetus; only 2 to 4 in 1,000 such women will have a negative test result and so be at risk of sensitisation because they would not be offered antenatal antiD immunoglobulin. NIPT for fetal RHD genotype is slightly less accurate among women with a Dnegative fetus; between 13 and 57 in 1,000 such women will have a positive test result and so be offered antenatal antiD immunoglobulin unnecessarily.
Analysis case
Number of studies
False-negative rate (at risk of sensitisation) estimate (% )
False-positive rate (unnecessary anti D) estimate (% )
Inconclusive treated as test positive (including Thurik et al. and Grande et al.)
Inconclusive treated as test positive (excluding Thurik et al. and Grande et al.)
Excluding all inconclusive test results
Studies only done in Bristol
Abbreviation: CI, confidence interval.
The analysis of the 3 Bristol studies gave a slightly lower false-negative rate (0.21%; 95% confidence interval  0.09 to 0.48) and a higher false-positive rate (5.73%; 95% CI 4.58 to 7.16) than analyses including other studies. This suggests that the Bristol high-throughput NIPT approach may use a different test threshold compared with the testing done in other studies; minimising false-negative findings, with a consequent increase in the false-positive rate.
There was considerable variation in rates of inconclusive tests across studies, ranging from 0.4% to 14.3%. The most likely causes for this variability are differences in how the NIPT was done (such as different numbers and types of exons considered) and differences in characteristics of study populations (for example, different proportions of women of black African family origin). Based on a meta-analysis, the average rate of inconclusive test results was estimated to be 4.0% (95% CI 1.5 to 10.3) if all studies reporting inconclusive results were included, and 6.7% (95% CI 3.7 to 11.7) if only the Bristol studies were included.
An analysis of the effect of the timing of high-throughput NIPT for fetal RHD genotype on diagnostic accuracy suggested that false-negative rates were higher before 11 weeks' gestation, and thereafter false-negative rates were consistent, irrespective of timing. The effect of the timing of high-throughput NIPT on the number of inconclusive test results suggested that the percentage of inconclusive results drops as the gestational age increases from 11 weeks.

## Assessment of clinical outcomes
Seven studies reported the clinical effectiveness of NIPT for fetal RHD genotype, all of which were observational and carried out in European countries. The sample size of the studies ranged from 284 to 15,126 and most participants were of white European family origin. Only 2 studies compared women having NIPT for fetal RHD genotype with controls (Tiblad et al. 2013; Banch Clausen et al. 2014). Tiblad et al. (2013) was considered to be at serious risk of bias, and Banch Clausen et al. (2014) was considered to be at critical risk of bias. The generalisability of these 2 studies to NHS clinical practice was limited because participants in the control group did not have routine antenatal antiD prophylaxis (RAADP). The other 5 studies only reported non-comparative-effectiveness data for women having NIPT for fetal RHD genotype. Data from these studies were supplemented with data from a UK audit on antiD immunoglobulin use (National comparative audit of blood transfusion: 2013 audit of anti-D immunoglobulin prophylaxis) for a comparison with current practice.
Tiblad et al. (2013) compared targeted RAADP in the first trimester with routine care (postpartum antiD prophylaxis only) in Sweden. They reported the incidence of D sensitisation in the cohort that had high-throughput NIPT for fetal RHD genotype as 0.26% (95% CI 0.15 to 0.36%; n=8347) compared with 0.46% (95% CI 0.37 to 0.56%; n=18,546) in the historical control cohort. High-throughput NIPT for fetal RHD genotype was associated with a significant risk reduction in sensitisation (unadjusted risk ratio  0.55; 95% CI 0.35 to 0.87) compared with historical controls. An updated analysis reported in a linked conference abstract (Neovius et al. 2015) found an adjusted odds ratio of 0.41 (95% CI 0.22 to 0.87).
Seven studies reported uptake rates of NIPT for fetal RHD genotype. Uptake rates ranged from 70% to more than 95% across the studies. In a pilot study done by Soothill et al. (2015) in 3 maternity services in the south-west of England, only 70% of eligible women joined the study in the first 6 months. The larger English study done by Chitty et al. (2014) reported that 88% of the 3,069 participants consented to have NIPT for fetal RHD genotype. The only country that reported nationwide uptake data was the Netherlands, where more than 95% of eligible women had NIPT for fetal RHD genotype. The studies generally noted that uptake is likely to increase over time if a nationwide screening programme is implemented.
The uptake of RAADP in women who accepted NIPT and had a positive result was reported in 4 studies and ranged from 86.0% to 96.1%. Of the larger studies, Van der Ploeg et al. (2015) reported nationwide data on women having NIPT for fetal RHD genotype in the Netherlands, where 96.1% of about 18,383 women with a positive test result had RAADP. Tiblad et al. (2013) reported a slightly lower rate, with 90% of 5,104 women with a positive NIPT result having RAADP. Data on the uptake of RAADP in women who had a negative test result, those who had an inconclusive test result, and those who refused NIPT for fetal RHD genotype, were limited. None of the studies reported whether all the women who had RAADP had the intended dosage at the intended time, or what proportion of women had additional antiD immunoglobulin because of a potentially sensitising event.
The uptake of postpartum antiD prophylaxis in women who accepted NIPT for fetal RHD genotype and had a positive test result was reported in 3 studies. Van der Ploeg et al. (2015) reported nationwide data on women having NIPT for fetal RHD genotype in the Netherlands, where 92% of about 18,383 women had postpartum antiD prophylaxis. A subgroup analysis by Banch Clausen et al. (2014) found slightly higher uptake of postpartum antiD prophylaxis among women who had NIPT (99.7%, 353/354) compared with those who did not have NIPT (95.7%, 66/69). Damkjaer et al. (2012) reported a similar rate among women who had NIPT (99.3%, 151/152). None of the included studies reported whether all women who had postpartum antiD prophylaxis had the intended dosage at the intended time.
Outcome measures relating to antiD immunoglobulin administration were reported in 3 noncomparative studies. Soothill et al. (2015) reported a significant 6% reduction per month in antiD immunoglobulin administration (95% CI 4 to 8) over a 6month period in 3 maternity services in the south west of England. The total use of antiD immunoglobulin fell by about 29%, corresponding to 35% of Dnegative women not having antiD immunoglobulin in their pregnancy unnecessarily. Similar results were also seen by Banch Clausen et al. (2014), who reported that 37.1% of women avoided unnecessary antiD immunoglobulin within 2 years of the introduction of a programme of NIPT for fetal RHD genotype. Grande et al. (2013) reported that, of 95 women carrying a Dnegative fetus, 5 women requested antiD immunoglobulin; so, unnecessary antiD immunoglobulin was avoided in 95% of women carrying a Dnegative fetus.
To better understand the likely consequences of implementing NIPT for fetal RHD genotype and basing antenatal antiD immunoglobulin administration on its results, the external assessment group did a simulation study. The following assumptions were made:
When needed, antenatal antiD immunoglobulin is offered at around 28 weeks.
Postpartum antiD prophylaxis is offered based on the result of cord blood typing.
Cord blood typing is 100% accurate.
There are no adverse consequences of giving antiD immunoglobulin.
The results of the simulation study, summarised in table 2, showed that using NIPT for fetal RHD genotype leads to a substantial reduction in RAADP use, from 99% of Dnegative women to 65.9%. This decline is similar in size to that seen by Soothill et al. (2015). The decrease is because of the drop (from 39% to 5.7%) in women with Dnegative fetuses needlessly having antiD immunoglobulin. Using NIPT for fetal RHD genotype means that about 1.2% of women miss having possibly beneficial RAADP, compared with 0.6% when using a universal RAADP approach with no testing.
Outcome
Treatment approach
Proportion of women
Antenatal antiD given
Universal antiD
Antenatal antiD given
Based on NIPT
Unnecessary antiD given (Dnegative fetus)
Universal antiD
Unnecessary antiD given (Dnegative fetus)
Based on NIPT
AntiD not given (Dpositive fetus)
Universal antiD
AntiD not given (Dpositive fetus)
Based on NIPT
Treatment approach
Proportion of women
Postpartum and emergency antiD only
Universal antiD
Based on NIPT with postpartum antiD
Based on NIPT with no postpartum antiD for women who test negative
Treatment approach
Proportion of women
Postpartum and emergency antiD only
Universal antiD
Based on NIPT with postpartum antiD based on cord blood typing
Based on NIPT with no postpartum antiD for women testing negative
Abbreviation: NIPT, non invasive prenatal testing.
Assuming all women still have postpartum cord blood typing and postpartum antiD prophylaxis if needed, the simulation study showed that NIPT would result in about 3 extra sensitisations per 100,000 women. If cord blood typing is not done, there would be about 13 extra sensitisations per 100,000 women. These increases are small compared with the total number of sensitisations because of antiD immunoglobulin failure and nonadherence to antiD immunoglobulin treatment (around 281 per 100,000 women), and compared with not using RAADP at all (around 641 per 100,000).
Results of the simulation study also showed that using NIPT for fetal RHD genotype is unlikely to have any meaningful effect on mortality in later pregnancies; if women with a negative NIPT result never have postpartum antiD prophylaxis, there would be about 5 extra fetal or neonatal deaths per 1 million Dnegative women. In current practice, there are an estimated 86 fetal or neonatal deaths per 1 million Dnegative women.

## Assessment of implementation issues
Twelve studies were identified in a review of implementation of NIPT for fetal RHD genotype. Most studies reported that NIPT for fetal RHD genotype was feasible. Several studies reported potential issues relating to implementation, such as adherence to the antiD prophylaxis programme. Some studies highlighted the importance of short transport times for samples and effective management of transporting samples. The need for greater awareness of NIPT among physicians and midwives was also identified in some studies.
A UK-based survey (Oxenford et al. 2013) showed that, although most of the women surveyed supported the implementation of NIPT, their current knowledge of Rh blood groups and antiD treatment was limited, which could be a barrier to implementation.

# Cost effectiveness

## Review of economic evidence
Seven studies were identified in a review of existing studies on the cost effectiveness of high-throughput NIPT to determine fetal RHD genotype in pregnant women who are D negative and are not sensitised to the D antigen. The quality of the included studies' findings was uncertain because they did not report the validity of the diagnostic accuracy outcomes used. The degree of uncertainty in the cost-effectiveness estimates was also difficult to establish.
Results across the existing economic studies were conflicting. Only 1 study found NIPT for targeting RAADP to be cost saving compared with nontargeted RAADP. Two studies reported that NIPT for fetal RHD genotype was cost saving compared with no RAADP, that is, compared with postpartum antiD prophylaxis only. Three studies reported that NIPT for fetal RHD genotype was not cost effective or was of no economic benefit. Only 1 study directly related to the UK (Szczepura et al. 2011).

## Modelling approach
The external assessment group developed a de novo economic model designed to assess the cost effectiveness of high-throughput NIPT to determine fetal RHD genotype in pregnant women who are D negative and are not sensitised to D antigen.
A decision tree cohort approach was developed to estimate the costs and health outcomes with and without high-throughput NIPT for fetal RHD genotype. The treatment part of the model was based closely on the economic model used in the NICE technology appraisal guidance on routine antenatal anti-D prophylaxis for women who are rhesus D negative, developed by researchers at the School of Health and Related Research (ScHARR).
In the model, a pregnant woman enters after being identified as D negative and not sensitised to D antigen, based on testing at first contact with the doctor or midwife, or at the booking appointment (at 8 to 12 weeks' gestation). The first part of the model divides the cohort according to fetal RHD genotype and treatment. This determines when having RAADP is appropriate, inappropriate, or unnecessary, and when avoidance of RAADP is potentially harmful. Test performance, adherence to high-throughput NIPT for fetal RHD genotype and RAADP, and the effectiveness of RAADP all inform the estimation of the probability of sensitisation. The second part of the model considers the short- and long-term consequences of sensitisations, such as fetal or neonatal death, and minor or major fetal development problems in later pregnancies.
Four alternative ways (see table 3) that using high-throughput NIPT may affect the existing postpartum care pathway were considered:
Postpartum scenario 1 (PP1): postpartum cord blood typing and fetomaternal haemorrhage testing would continue to be done, based on current guidelines, in all women regardless of the fetal RHD genotype identified with high-throughput NIPT.
Postpartum scenario 2 (PP2): postpartum cord blood typing and fetomaternal haemorrhage testing (and by implication antiD immunoglobulin) would be withheld if high-throughput NIPT for fetal RHD genotype identified a Dnegative fetus, but would continue to be done if high-throughput NIPT was inconclusive or had identified a Dpositive fetus.
Postpartum scenario 3 (PP3): postpartum cord blood typing would be done if high-throughput NIPT for fetal RHD genotype identified a Dnegative fetus. Fetomaternal haemorrhage testing and post-delivery antiD immunoglobulin would be provided if high-throughput NIPT was inconclusive or identified a Dpositive fetus.
Postpartum scenario 4 (PP4): postpartum cord blood typing would not be carried out in any women. Fetomaternal haemorrhage testing and post-delivery antiD immunoglobulin would be provided if high-throughput NIPT was inconclusive or had identified a Dpositive fetus.
Scenario
High-throughput NIPT result
Cord blood typing
FMH testing
Postpartum antiD
Postpartum scenario 1
Any
Yes
Yes if CBT+
As guided by CBT and FMH testing
Postpartum scenario 2
Negative
No
No
No
Postpartum scenario 2
Positive or inconclusive
Yes
Yes if CBT+
As guided by CBT and FMH testing
Postpartum scenario 3
Negative
Yes
Yes if CBT+
As guided by CBT and FMH testing
Postpartum scenario 3
Positive or inconclusive
No
Yes
Yes with additional dose per FMH test
Postpartum scenario 4
Negative
No
No
No
Postpartum scenario 4
Positive or inconclusive
No
Yes
Yes with additional dose per FMH test
Abbreviations: CBT, cord blood typing; NIPT, non invasive prenatal testing; FMH, fetomaternal haemorrhage; +, positive.
The annual number of pregnancies in Dnegative women in England was estimated to be 99,225. This represents a cross section of all pregnancies, and the proportions of first, second, third and later pregnancies are used to characterise the total fertility rate of a typical Dnegative woman. This estimate was based on a birth rate of 12.2 per 1,000 women per year and assumes that 15% of the population is D negative. The proportion of Dpositive babies born to women who are D negative was estimated as 61.6%. This rate was applied across all pregnancies, that is, the first and later pregnancies.
The diagnostic accuracy of high-throughput NIPT for fetal RHD genotype and the proportion of inconclusive results were based on the meta-analyses done in the clinical-effectiveness assessment. The base case used the pooled results for the subgroup of UK (Bristol-based) studies in which inconclusive results were considered as test positive. These studies were considered the most relevant to NHS clinical practice. Sensitivity was 0.998 (95% CI 0.992 to 0.999), specificity was 0.942 (95% CI 0.920 to 0.959) and the rate of inconclusive results was 6.7%.
For consistency, this diagnostics assessment used the clinical effectiveness of RAADP that was established in the NICE technology appraisal guidance on routine antenatal anti-D prophylaxis for women who are rhesus D negative. Evidence for the clinical effectiveness of postpartum antiD prophylaxis was taken from a Cochrane review (Crowther et al. 1997). The clinical-effectiveness estimates are presented in table 4.
Outcome
NICE guidance on routine antenatal antiD prophylaxis for women who are rhesus D negative
Crowther et al. (1997; sensitisation 6 months after delivery)
Odds ratio: sensitisation with RAADP (compared with no RAADP, conditional on having postpartum antiD prophylaxis) (95% CI)
(0.21 to 0.65)
Odds ratio: sensitisation at birth, follow-up up to 6 months, with postpartum antiD prophylaxis (compared with no postpartum antiD prophylaxis, conditional on no RAADP) (95% CI)
(0.06 to 0.11)
Sensitisation rate without RAADP (conditional on having postpartum antiD prophylaxis) (95% CI)
(0.18 to 1.71)
(0.18 to 1.71) Baseline sensitisation rate of no RAADP assumed the same
Sensitisation rate with RAADP (95% CI)
(0.29 to 0.40)
Sensitisation rate without RAADP and without postpartum antiD prophylaxis (95% CI)
(8.0 to 13.8)
Abbreviations: CI, confidence interval; RAADP, routine antenatal antiD prophylaxis.
The number of potentially sensitising events was taken from the recent UK audit on antiD immunoglobulin use (National comparative audit of blood transfusion: 2013 audit of anti-D immunoglobulin prophylaxis). The probability of women having at least 1 (reported) potentially sensitising event was estimated as 15.5%. Of these, 69.3% were estimated to have had a fetomaternal haemorrhage test and 95.8% were estimated to have had antiD immunoglobulin after the event. It was estimated that about 80% of these events happened after 20 weeks' gestation, and it was assumed that these events were treated with the minimum required dose of 500 IU antiD immunoglobulin. For the remaining 20% of events (before 20 weeks' gestation), it was assumed that women had the minimum required dose of 250 IU antiD immunoglobulin.
The National comparative audit of blood transfusion: 2013 audit of antiD immunoglobulin prophylaxis was used to provide estimates of adherence to RAADP. It reported that, out of all eligible women: 99% had at least 1 RAADP injection; full adherence (that is the correct dose at the correct time) was better with the single-dose regimen (90%) compared with the 2dose regimen (59%); 98.4% had postpartum antiD prophylaxis; and 96% had antiD immunoglobulin for documented potentially sensitising events. Within the economic model, it was assumed that adherence to RAADP was 99.0% and that adherence to postpartum antiD prophylaxis was 98.4%. There was limited evidence on adherence to NIPT for fetal RHD genotype, so it was assumed that using NIPT has no additional effect on adherence to antiD prophylaxis.
The effects of sensitisation on later pregnancies were taken from Finning et al. (2008) and the NICE technology appraisal guidance on routine antenatal anti-D prophylaxis for women who are rhesus D negative. The proportion of fetal or neonatal deaths was estimated to be 5%; and the proportion of babies affected with minor or major developmental problems was estimated to be 6% or 5% respectively. Minor developmental problems were estimated to last 16 years and the life expectancy for a person with major developmental problems was estimated to be 59.5 years.
The estimated cost of high-throughput NIPT for fetal RHD genotype included consumables, staffing, equipment, and indirect and overhead costs. The estimated cost was based on testing at full capacity, that is, dealing with at least 100,000 samples per year. The unit cost per sample may vary, because it is a function of capacity and the annual predicted level of usage of each testing machine. Also, a royalty fee is under negotiation and will need to be added to the cost of the test. The cost of high-throughput NIPT for fetal RHD genotype remains commercial in confidence at the time of writing this diagnostics guidance.
The cost of antiD immunoglobulin was taken from the British national formulary. Currently 2 brands (DGam and Rhophylac) and 4 doses (250-, 500-, 1,500- and 2,500unit vials) are available. Weighted averages based on recommended dose regimens and market share were calculated. The estimated costs were: 31.69 for antiD immunoglobulin for potentially sensitising events; 41.58 for RAADP; and 35.69 for postpartum antiD prophylaxis. The cost of giving antiD immunoglobulin was set to 5.
In current practice, cord blood typing is done to confirm the baby's Rh blood group, and maternal blood samples are tested for fetomaternal haemorrhage after birth. The costs, updated to 2015 prices, for cord blood typing (4.18) and associated phlebotomy (3.32) were taken from Szczepura et al. (2011). The cost of fetomaternal haemorrhage testing by flow cytometry was estimated to be 128.10.
The relevant interventions for maternal and neonatal sensitisation were taken from the NICE technology appraisal guidance on routine antenatal anti-D prophylaxis for women who are rhesus D negative. Unit costs were taken from the NHS reference costs 2014/15. This resulted in an estimated average total cost per sensitisation of 3,167. The estimated annual costs for minor (111) and major (574) development problems were also assumed to be the same as in the NICE technology appraisal guidance (updated to 2015 prices).
The following utilities were assumed in the model: minor developmental problems, 0.85; major developmental problems, 0.42; and general population, 0.88. These values are the same as those used in the NICE technology appraisal guidance on routine antenatal anti-D prophylaxis for women who are rhesus negative.

## Base-case results
Key assumptions made in the model were:
Sensitisations do not affect the pregnancy in which they occur.
AntiD immunoglobulin used within 1 pregnancy has no effect in reducing sensitisations during the next pregnancy.
The proportion of Dnegative women is based on estimates from people of white European family origin.
The proportion of Dpositive babies born to Dnegative women is assumed to be the same irrespective of pregnancy number.
The number of Dpositive babies in the model is determined by combining the probability, in the general population of Dnegative women, of having a Dpositive baby (61.6%) with the sensitivity and specificity of NIPT (in which inconclusive results are treated as test positive).
The probability of having a Dpositive baby in women with inconclusive test results is based on the pooled probability in the study populations used to inform the diagnostic accuracy estimate.
All NIPT is assumed to be done early enough to determine the need for RAADP at 28 weeks' gestation.
RAADP is only offered to women in whom the NIPT result indicates that their fetus is D positive or in whom the results are inconclusive.
Women with an inconclusive NIPT result are treated the same as women who test positive in terms of RAADP, and tests and treatment after potentially sensitising events.
Women offered RAADP will also be offered supplementary antiD immunoglobulin at the minimum dose needed for any potentially sensitising events.
Potentially sensitising events that involve fetal death are assumed to be independent of previous sensitisation within the same pregnancy.
Women with false-negative test results indicated by cord blood typing and who have postpartum antiD prophylaxis are assumed to have a sensitisation rate of 0.95%.
Adherence to RAADP is assumed to be the same with and without NIPT; similarly, adherence to postpartum antiD prophylaxis is assumed to be the same with or without NIPT.
There are no adverse health effects from using antiD immunoglobulin.
Results show that all NIPT strategies cost less, but are less effective than the comparator, current clinical practice (table 5). Strategies PP1 and PP3 are associated with smaller quality-adjusted life year (QALY) losses than PP2 and PP4. This is because in both PP1 and PP3, cord blood typing is used to identify false-negative results, which would allow women who had been incorrectly identified as having a Dnegative baby, and so had not been offered RAADP, to have postpartum antiD prophylaxis. This would reduce the number of sensitisations, therefore reducing QALY losses.
Strategies
Total costs
Total QALYs
Incremental costs
Incremental QALYs
ICER
( saved/ QALY lost)
No test and RAADP (current practice)
N/A
N/A
N/A
Postpartum scenario 1 versus no test and RAADP
Postpartum scenario 2 versus no test and RAADP
Postpartum scenario 3 versus no test and RAADP
Postpartum scenario 4 versus no test and RAADP
Abbreviations: ICER, incremental cost-effectiveness ratio; QALY, quality-adjusted life year; RAADP, routine antenatal anti D prophylaxis.
The variations in costs between the 4 strategies were mainly driven by different postpartum testing costs and postpartum antiD prophylaxis costs. The added cost of managing sensitisations and their associated health consequences in later pregnancies was largest for the strategies with more sensitisations (PP2 and PP4), and was very small for strategies PP1 and PP3.
In the fully incremental analysis of NIPT for fetal RHD genotype for the different postpartum testing strategies, PP3 and PP4 were dominated. Strategy PP4 was dominated by strategy PP2 because it had the same number of QALYs but was more expensive than PP2. Strategy PP3 was dominated by strategy PP1 because it had the same number of QALYs but was more expensive than PP1.
The cost-effectiveness acceptability curve showed that PP1 had the highest probability of being cost effective, with 0.65 and 0.73 for maximum acceptable incremental cost-effectiveness ratio (ICER) values of 20,000 and 30,000 per QALY gained respectively. For the same maximum acceptable ICER values, the probability of PP2 being cost effective was 0.30 and 0.22 respectively.

## Sensitivity and scenario analyses
Sensitivity analyses showed that the results of the economic model are robust to small changes in the clinical effectiveness of RAADP, the timing of testing (between 11 and 23 weeks) and adherence to antiD immunoglobulin treatment.
A sensitivity analysis was done on the diagnostic accuracy of NIPT. When the diagnostic accuracy of NIPT was based on the meta-analysis of all studies rather than the Bristol studies alone, specificity increased by 2%, sensitivity decreased by 0.2%, the total cost across all NIPT strategies reduced, but total QALYs were only marginally affected. PP1 and PP3 remained the most cost-effective strategies.
In a sensitivity analysis on the rates of inconclusive results, NIPT became less cost effective as the rate of inconclusive results increased, but strategies PP1 and PP3 always remained more cost effective than current practice. When the rate of inconclusive results was low, PP3 became the most cost-effective strategy. When the rate of inconclusive results was high, PP1 became the most cost-effective strategy.
A 2way sensitivity analysis was done on test and treatment costs. The unit cost of NIPT is subject to uncertainty because it depends on throughput (the annual total number of samples analysed) and the level of the royalty fee. Similarly, the cost of antiD immunoglobulin may differ from the list price depending on negotiated discounts. The results of a 2way analysis on these unit costs showed that the base case is very sensitive to both the price of NIPT and the price of antiD immunoglobulin. A small increase in price of high-throughput NIPT or a small fall in the price of antiD immunoglobulin would result in current practice becoming more cost effective than NIPT strategies.
The cost of high-throughput NIPT for fetal RHD genotype was uncertain when this diagnostics guidance was written because it is highly dependent on the number of tests processed. The external assessment group did a threshold analysis to identify the point at which the test would move from being considered cost effective to being considered not cost effective, using a maximum acceptable ICER of 20,000 per QALY gained. Results show that raising the cost for high-throughput NIPT to 24.64 or more would result in current practice becoming more cost effective than NIPT strategies.
A sensitivity analysis was done on the cost of fetomaternal haemorrhage testing. Reducing the cost of a fetomaternal haemorrhage test to 3.17 (Szczepura et al. 2011; updated to 2015 prices) halved the estimated total costs of all strategies when compared with the total costs of the base-case scenarios, with total QALYs remaining similar to base-case results. When the cost of fetomaternal haemorrhage test was reduced, PP2 and PP4 became less cost effective than current practice, whereas PP1 and PP3 remained more cost effective compared with current practice.
An alternative postpartum-testing strategy to those included in the scope was assessed. The strategy separated women in whom NIPT identified a Dpositive fetus from women in whom NIPT gave an inconclusive result (and were therefore treated as if the fetus was Dpositive). Cord blood typing was done for women identified as having either a Dnegative fetus by NIPT or who had an inconclusive NIPT result, but not done for women in whom NIPT indicated a Dpositive fetus, and resulted in total costs of 15,230,372 and 2,433,756 QALYs per 100,000 pregnancies. This postpartum approach dominated all other NIPT strategies, and the ICER for this strategy compared with current practice was 1,638,356 saved per QALY lost.# Committee discussion

# Current practice
The committee considered the current standard of care offered to pregnant women who are rhesusD (D) negative. It heard from clinical experts on the committee that current care for women who are not sensitised to the D antigen involves routine antenatal antiD prophylaxis, additional doses of antiD immunoglobulin if a woman has a potentially sensitising event, and postpartum testing of cord blood and antiD prophylaxis if cord blood typing shows the baby to be D positive. The committee noted that introducing these methods for preventing sensitisation of women to the D antigen has dramatically reduced the number of sensitisations and the rates of haemolytic disease of the fetus and newborn over the last 40 years. The committee also heard from a clinical expert that there are effective treatments for Dnegative women who are sensitised to D antigen, which means that deaths from severe haemolytic disease of the fetus and newborn are very rare.
The committee considered whether there were any problems with the current care offered to pregnant women who are D negative and not sensitised to the D antigen. It heard from a clinical expert that errors do sometimes occur, for example, a small number of women at risk of sensitisation do not have antiD immunoglobulin, or do not receive the correct dose of antiD immunoglobulin at the correct time. The committee also heard from a clinical expert that many sensitisations result from clinically silent fetomaternal haemorrhage events  potentially sensitising events without a known cause or clinical symptoms. The committee further heard that cord blood typing to determine the Rh blood group of the baby after birth may be affected by errors, such as sampling the blood of the mother instead of the baby, or incorrect sample labelling. The committee concluded that although antiD prophylaxis is very effective for reducing sensitisations and therefore haemolytic disease of the fetus and newborn, it is not perfect because sensitisations do still happen.
The committee considered the possible disadvantages of using antiD immunoglobulin. It heard from experts that there have previously been shortages of supply because it is a blood product and therefore a finite resource. The committee also considered the potential future risks from unknown prions or pathogens associated with using a blood product such as antiD immunoglobulin. The committee concluded that it would be beneficial to conserve supplies by only using antiD immunoglobulin for those in whom it is necessary.
The committee heard from a patient expert that for some women, having antiD immunoglobulin may not be acceptable for personal, cultural or religious reasons. It noted that using high-throughput noninvasive prenatal testing (NIPT) for fetal RHD genotype would allow women whose fetus was identified as D negative to avoid having unnecessary antiD immunoglobulin, while women identified as having a Dpositive fetus would be able to make an informed decision about whether to have antiD immunoglobulin.

# Clinical effectiveness
The committee considered the diagnostic performance of high-throughput NIPT for fetal RHD genotype. It noted that good-quality evidence was available and that the test is accurate after 11 weeks of gestation. The committee then considered how the diagnostic accuracy of the test affected clinical effectiveness. It noted that there is a small increase in the false-negative rate for high-throughput NIPT to determine fetal RHD genotype (0.21%; 95% CI  0.09 to 0.48), compared with the current practice of postpartum cord blood typing. This means that some women with a Dpositive fetus would be incorrectly identified as having a Dnegative fetus and would not be offered routine antenatal antiD prophylaxis (RAADP) or antiD immunoglobulin after potentially sensitising events. Because of this, more women could become sensitised to the D antigen and may have complications in later pregnancies, although the committee heard from a clinical expert that the severity of these complications is hard to predict. The committee noted that the rate of sensitisations with current practice was estimated to be 281 per 100,000 Dnegative pregnancies. If offering RAADP and antiD immunoglobulin after potentially sensitising events was based on the results from NIPT for fetal RHD genotype, the rate of sensitisations would increase by 3, to 284 sensitisations per 100,000 Dnegative pregnancies. The committee considered that this relatively small increase in the number of sensitisations could be accepted in the context of other potential benefits of NIPT associated with avoiding unnecessary treatment with blood products.
The committee considered the results of the economic model. It noted that the quality-adjusted life year (QALY) losses in the model were 0.46 per 100,000 pregnancies if the postpartum testing strategy stayed the same as current practice (cord blood typing for all Dnegative women regardless of the NIPT result). The committee noted that although this is a reduction in clinical effectiveness compared with current practice, the reduction is extremely small (0.0000046 QALYs per pregnancy). The committee therefore concluded that the clinical effectiveness of using high-throughput NIPT for fetal RHD genotype to guide antenatal antiD prophylaxis is comparable with offering antenatal antiD prophylaxis to all Dnegative women, provided that there are no changes to postpartum practice.

# Cost effectiveness
The committee considered the cost savings in the economic model. It noted that cost savings in the models were 583,538 per 100,000 pregnancies in Dnegative women if the postpartum testing strategy stayed the same as current practice (cord blood typing for all Dnegative women regardless of the NIPT result, referred to as postpartum scenario 1  in the economic analysis). The committee noted that the cost savings are relatively small, at 5.84 per pregnancy, and on their own might not justify the risks that could be associated with making substantial changes to current practice. The committee then considered the base-case incremental cost-effectiveness ratio (ICER) for PP1. It noted that although the ICER appears to be large, at 1,269,100 saved for each QALY lost, it is very sensitive to changes in the numerator (change in cost) or denominator (change in QALYs), and is therefore subject to substantial uncertainty. The committee concluded that the total costs for using high-throughput NIPT for fetal RHD genotype to guide antenatal antiD prophylaxis are not substantially different from the total costs for the current practice of offering antenatal antiD prophylaxis to all Dnegative women, provided that there are no changes to postpartum practice.
The committee considered the different postpartum testing strategies presented in the diagnostics assessment report (see section 4.24). It noted that in the base-case analysis, NIPT using PP1 was the most cost-effective strategy compared with current practice. The committee heard from clinical experts that the postpartum care in PP1 is the same as used in current clinical practice. It also noted that with different assumptions on postpartum testing, other postpartum scenarios could be associated with greater cost savings, but increased QALY losses compared with PP1. The committee concluded that it is preferable to minimise the QALY losses.
The committee considered the results of a scenario analysis that made different assumptions on postpartum testing (PP5). It noted that this postpartum scenario was associated with greater cost savings and equivalent QALY losses compared with PP1. The committee heard from clinical experts that postpartum testing involves taking a cord blood sample soon after the birth, and that although midwives are used to doing this they also have multiple other tasks to complete at this time. The committee was concerned that if midwives had to get the NIPT result and then make a decision on whether to take a cord blood sample in the period immediately after the delivery, errors could be made, for example, not taking a cord blood sample from a fetus predicted to be D negative. The committee concluded that although alternative postpartum strategies may potentially have greater cost savings, they would be complicated to implement in clinical practice and may result in errors, which could affect costs and clinical effectiveness. The committee also discussed an alternative approach in which cord blood samples would be taken from all babies born to Dnegative women and the laboratory would then decide whether to test the cord blood sample. The committee concluded that the postpartum testing of cord blood should not be changed from current practice. This is because without cord blood typing, false-negative NIPT results would not be identified and women with false-negative NIPT results would not have postpartum antiD prophylaxis. The committee noted the difficulties of taking a blood sample from the cord and that the consequences of a sampling error may include having to take repeat blood samples from a neonate. It decided that further research on the practicalities of implementing alternative postpartum testing strategies would be valuable (see section 6.2).
The committee discussed the input used in the model for the cost of care of a pregnant woman who has been sensitised to the D antigen in an earlier pregnancy. It heard from a clinical expert that some women who are sensitised to the D antigen will be identified as having a Dnegative fetus, and others will be identified as having a Dpositive fetus, but will not experience problems during their pregnancy. These 2 groups of women would not need many extra appointments with a specialist obstetrician. A third group of sensitised women will be identified as having a Dpositive fetus and will experience problems during their pregnancy. These women will need more frequent surveillance and treatment for the baby before and after the birth. The committee concluded that if a weighted average is taken of the cost of care for these 3 groups of pregnant women, then an input of 3,167 per sensitised pregnancy is reasonable.
The committee considered the cost of the test that was used in the economic model and noted that the cost did not include sample transport. It heard from the current provider of the test, the International Blood Group Reference Laboratory (IBGRL), that blood samples are transported around the country to their laboratory on a daily basis using the NHS Blood and Transplant (NHSBT) transport network. It heard further, that because of this established transport network, there should be no cost for sample transport. The committee was concerned that although there may be no cost for sample transport between the NHSBT units and the IBGRL, there may be a cost for transporting the sample from the maternity clinic to the NHSBT unit. It was also concerned about the length of time it may take to transport samples from rural areas to the IBGRL, and that longer sample transport times may result in increased rates of failed tests. The committee also heard from the IBGRL that the unit cost of the test depends on the expected annual sample throughput and on a royalty fee, which is currently under negotiation. The committee concluded that the test cost is uncertain.
The committee considered whether there were any costs associated with implementing high-throughput NIPT for fetal RHD genotype that had not been included in the economic model. It noted that extra time to explain the test, take the blood sample, give the test results, and provide counselling, that could result in extra midwife appointments, were not included in the model. The committee heard from a clinical expert that in the south-west of England where high-throughput NIPT for fetal RHD genotype has been implemented, the blood sample for the test is normally taken at the routine 16week antenatal appointment; therefore, no additional appointments are needed. It also heard from the clinical expert that the main issue when implementing the test was educating midwives and other healthcare professionals so they understood the test and could explain it to women and their families. It noted that a patient information leaflet explaining the test and its results is available from NHSBT. The committee heard from the external assessment group that none of the studies in the review of implementation, included costs associated with implementation. The committee concluded that the costs associated with implementing high-throughput NIPT for fetal RHD genotype were uncertain.
The committee considered a threshold analysis done by the external assessment group on the unit cost of the test. It noted that results show that the cost effectiveness of high-throughput NIPT for fetal RHD genotype is sensitive to small increases in costs associated with doing the test, for example, sample transport, the need for repeat tests, midwife time, or the cost of the test itself. The committee also noted that increasing the test cost to 24.64 or more per test would result in high-throughput NIPT for fetal RHD genotype no longer being cost effective compared with current practice, using a maximum acceptable ICER of 20,000 per QALY gained. The committee concluded that high-throughput NIPT for fetal RHD genotype has the potential to be cost effective, but that the cost savings are volatile with respect to the cost of the test (see section 5.11) and the costs associated with implementation (see section 5.12). The committee also concluded that the overall cost of testing below which high-throughput NIPT for fetal RHD genotype can be considered cost effective should not be stated to 2 decimal places in the recommendation. This is because there is substantial uncertainty about the results of the model. The committee decided that 24.64 should be rounded down to 24 rather than up to 25 to increase the chance of high-throughput NIPT for fetal RHD genotype being cost effective.

# Other considerations
The committee noted its conclusions on the comparable clinical effectiveness of high-throughput NIPT for fetal RHD genotype and current practice (see section 5.6), and the uncertainty about cost savings (see section 5.13). The committee also noted its conclusion that it would be beneficial to avoid inappropriate use of antiD immunoglobulin (see section 5.3). The committee decided that although the cost savings are potentially small, recommending high-throughput NIPT for fetal RHD genotype would be an effective way of reducing unnecessary use of antiD immunoglobulin, and that this reduction could affect a large number of women.
The committee considered the effect that ethnicity has on NIPT results. They heard from the provider of the test, IBGRL, that Dnegative women of black African family origin are more likely to have an RHD pseudogene, and so are more likely to have an inconclusive or false-positive NIPT result compared with women from other ethnic family origins. The committee noted that women with an inconclusive or false-positive NIPT result would be offered antenatal antiD prophylaxis (that is, they would have the same care as they would have in current practice), and so would not be at a greater risk of sensitisation to the D antigen than women from other ethnic family origins. It noted further that although unnecessary antiD immunoglobulin use would be reduced in women of black African family origin, these women would be more likely to have unnecessary antiD immunoglobulin than women of white European family origin. The committee concluded that this is a proportionate means of achieving a reduction in antiD immunoglobulin use in the population as a whole.
The committee considered the current level of interest in high-throughput NIPT for fetal RHD genotype. It heard from a clinical expert that there have been many enquiries about the test from healthcare professionals and women who would like to have the test but do not live in an area where it has been implemented. It also heard from another clinical expert that the level of knowledge and understanding of NIPT is growing because of the publicity around NIPT for Down's syndrome and other aneuploidies. The committee concluded that based on the current level of interest, the timing was right for making a recommendation of high-throughput NIPT for fetal RHD genotype, but noted that additional data collection from areas beginning to implement the test would help confirm the cost of implementing the test given the uncertainty about this.# Recommendation for further research
Data collection and analysis of the costs and resource use associated with implementing high-throughput noninvasive prenatal testing for fetal RHD genotype is recommended to show the overall cost of testing and to inform any future update of the guidance. This may include costs and resource use associated with:
training for healthcare professionals
explaining the test to women and their families
test failures
blood sampling, giving results and counselling when needed
sample transport and management
record keeping
adherence to high-throughput noninvasive prenatal testing and antenatal antiD prophylaxis.
Further research is recommended on alternative postpartum testing strategies that do not include cord blood typing of all babies born to rhesusD (D) negative women. This may include:
an audit of D results from cord blood typing compared with results from high-throughput NIPT for fetal RHD genotype
research on the practicalities of implementing alternative postpartum testing strategies.