Abstract: Nineteen trials involving 10,667 women were included. Risk of bias in trials was difficult to assess accurately due to incomplete reporting. None of the evidence relating to our main outcomes was graded as high quality. The quality of evidence was downgraded due to missing information on trial methods, imprecision in risk estimates and heterogeneity. Eighteen of these studies compared the use of Doppler ultrasound of the umbilical artery of the unborn baby with no Doppler or with cardiotocography (CTG). One more recent trial compared Doppler examination of other fetal blood vessels (ductus venosus) with computerised CTG. The use of Doppler ultrasound of the umbilical artery in high-risk pregnancy was associated with fewer perinatal deaths (risk ratio (RR) 0.71, 95% confidence interval (CI) 0.52 to 0.98, 16 studies, 10,225 babies, 1.2% versus 1.7 %, number needed to treat (NNT) = 203; 95% CI 103 to 4352, evidence graded moderate). The results for stillbirths were consistent with the overall rate of perinatal deaths, although there was no clear difference between groups for this outcome (RR 0.65, 95% CI 0.41 to 1.04; 15 studies, 9560 babies, evidence graded low). Where Doppler ultrasound was used, there were fewer inductions of labour (average RR 0.89, 95% CI 0.80 to 0.99, 10 studies, 5633 women, random-effects, evidence graded moderate) and fewer caesarean sections (RR 0.90, 95% CI 0.84 to 0.97, 14 studies, 7918 women, evidence graded moderate). There was no comparative long-term follow-up of babies exposed to Doppler ultrasound in pregnancy in women at increased risk of complications. No difference was found in operative vaginal births (RR 0.95, 95% CI 0.80 to 1.14, four studies, 2813 women), nor in Apgar scores less than seven at five minutes (RR 0.92, 95% CI 0.69 to 1.24, seven studies, 6321 babies, evidence graded low). Data for serious neonatal morbidity were not pooled due to high heterogeneity between the three studies that reported it (1098 babies) (evidence graded very low). The use of Doppler to evaluate early and late changes in ductus venosus in early fetal growth restriction was not associated with significant differences in any perinatal death after randomisation. However, there was an improvement in long-term neurological outcome in the cohort of babies in whom the trigger for delivery was either late changes in ductus venosus or abnormalities seen on computerised CTG. Current evidence suggests that the use of Doppler ultrasound on the umbilical artery in high-risk pregnancies reduces the risk of perinatal deaths and may result in fewer obstetric interventions. The results should be interpreted with caution, as the evidence is not of high quality. Serial monitoring of Doppler changes in ductus venosus may be beneficial, but more studies of high quality with follow-up including neurological development are needed for evidence to be conclusive.

Plain-language summary: We searched for evidence in March 2017. We found 19 trials involving over 10,000 women. Eighteen of these studies compared the use of Doppler ultrasound of the umbilical artery of the unborn baby with no Doppler or with cardiotocography (CTG, sometimes called electronic fetal monitoring). One more recent trial compared Doppler examination of other fetal blood vessels (ductus venosus) with computerised CTG (short-term variation). Evidence from included studies was assessed as moderate to very low-quality due to incomplete reporting of methods and uncertainty of findings; when the strength of the evidence is low or very low, this means future research may change the results and we cannot be certain about them. Results showed that Doppler ultrasound of the umbilical artery may decrease the number of babies who die, and may lead to fewer caesarean sections and inductions of labour. There was no clear difference in the number of stillbirths, births using forceps or ventouse, or babies with a low Apgar score five minutes after birth. Findings for serious problems in the neonate were not consistent in different studies. In babies with growth restriction, when the decision to deliver was based on late ductus venosus changes or abnormalities on computerised CTG, this appeared to improve long-term (two-year) developmental outcome. Doppler ultrasound in high-risk pregnancies appears to reduce the number of babies who die, and may also lead to fewer obstetric interventions. However, the evidence was of moderate to very low-quality. Further studies of high-quality with long-term follow-up would help us to be more certain.