Investigation and Care of a Small‐for‐Gestational‐Age Fetus and a Growth Restricted Fetus (Green‐top Guideline No. 31)
Authors: Morris R. Katie , Johnstone Edward , Lees Christoph , Morton Victoria , Smith Gordon ,   the Royal College of Obstetricians and Gynaecologists
Published: May 2024

Key recommendations

All women should be assessed at booking (by 14 weeks) for risk factors for fetal growth restriction (FGR) to identify those who require increased surveillance using an agreed pathway [Grade GPP]. Findings at the midtrimester anomaly scan should be incorporated into the fetal growth risk assessment and the risk assessment updated throughout pregnancy. [Grade GPP]

Reduce smoking in pregnancy by identifying women who smoke with the assistance of carbon monoxide (CO) testing and ensuring in‐house treatment from a trained tobacco dependence advisor is offered to all pregnant women who smoke, using an opt‐out referral process. [Grade GPP]

Women at risk of pre‐eclampsia and/or placental dysfunction should take aspirin 150 mg once daily at night from 12+0–36+0 weeks of pregnancy to reduce their chance of small‐for‐gestational‐age (SGA) and FGR. [Grade A]

Uterine artery Dopplers should be carried out between 18+0 and 23+6 weeks for women at high risk of fetal growth disorders [Grade B]. In a woman with normal uterine artery Doppler and normal fetal biometry at the midtrimester scan, serial ultrasound scans for fetal biometry can commence at 32 weeks. Women with an abnormal uterine artery Doppler (mean pulsatility index > 95th centile) should commence ultrasound scans at 24+0–28+6 weeks based on individual history. [Grade B]

Women who are at low risk of FGR should have serial measurement of symphysis fundal height (SFH) at each antenatal appointment after 24+0 weeks of pregnancy (no more frequently than every 2 weeks). The first measurement should be carried out by 28+6 weeks. [Grade C]

Women in the moderate risk category are at risk of late onset FGR so require serial ultrasound scan assessment of fetal growth commencing at 32+0 weeks. For the majority of women, a scan interval of four weeks until birth is appropriate. [Grade B]

Maternity providers should ensure that they clearly identify the reference charts to plot SFH, individual biometry and estimated fetal weight (EFW) measurements to calculate centiles. For individual biometry measurements the method used for measurement should be the same as those used in the development of the individual biometry and fetal growth chart [Grade GPP]. For EFW the Hadlock three parameter model should be used. [Grade C]

Maternity providers should ensure that they have guidance that promotes the use of standard planes of acquisition and calliper placement when performing ultrasound scanning for fetal growth assessment. Quality control of images and measurements should be undertaken. [Grade C]

Ultrasound biometry should be carried out every 2 weeks in fetuses identified to be SGA [Grade C]. Umbilical artery Doppler is the primary surveillance tool and should be carried out at the point of diagnosis of SGA and during follow‐up as a minimum every 2 weeks. [Grade B]

In fetuses with an EFW between the 3rd and 10th centile, other features must be present for birth to be recommended prior to 39+0 weeks, either maternal (maternal medical conditions or concerns regarding fetal movements) or fetal compromise (a diagnosis of FGR based on Doppler assessment, fetal growth velocity or a concern on cardiotocography [CTG]) [Grade C]. For fetuses with an EFW or abdominal circumference less than the 10th centile where FGR has been excluded, birth or the initiation of induction of labour should be considered at 39+0 weeks after discussion with the woman and her partner/family/support network. Birth should occur by 39+6 weeks. [Grade B]

Pregnancies with early FGR (prior to 32+0 weeks) should be monitored and managed with input from tertiary level units with the highest level neonatal care. Care should be multidisciplinary by neonatology and obstetricians with fetal medicine expertise, particularly when extremely preterm (before 28 weeks) [Grade GPP]. Fetal biometry in FGR should be repeated every 2 weeks [Grade B]. Assessment of fetal wellbeing can include multiple modalities but must include computerised CTG and/or ductus venous. [Grade B]

In pregnancies with late FGR, birth should be initiated from 37+0 weeks to be completed by 37+6 weeks [Grade A]. Decisions for birth should be based on fetal wellbeing assessments or maternal indication. [Grade GPP]