FM06 Estimated fetal weight at the 20 week anatomy scan: a predictor of SGA?
Fetal Medicine
Information
OBJECTIVE RCOG guidelines1 recommend assessment of estimated fetal weight (EFW) at the 2nd trimester anatomy scan, but there is as yet little information about the effectiveness in predicting fetuses that are small for gestational age (SGA) in third trimester and at birth.
METHODS We analysed data from the 7 NHS trusts in the GAP programme that recorded their anatomy scans routinely. We included all singleton pregnancies from June 2024 to December 2025 that had a subsequent scan between 24+0 and 32+0 weeks gestation, and assessed the second trimester scan’s ability to predict SGA (<10th centile) in the 3rd trimester and at birth. All centiles were calculated using the GROW standard without sex adjustment, and we determined positive predictive value (PPV) and relative risk with 95% Confidence Interval (RR, CI)
RESULTS There were 8438 pregnancies in the 7 units over the study period with a scan EFW at anatomy scan at a median of 20+1 weeks. 211 (2.5%) fetuses were SGA, of which 177 (83.9%) were followed up with a scan at an average of 28+2 weeks. 65 of these fetuses were also SGA at the follow up scan (PPV: 36.7%, RR: 7.1 CI: 5.7-9.0). For SGA at birth (median gestational age 38+4 weeks), the PPV of SGA at anatomy scan was 31.6% (RR: 2.4; CI 1.9-3.1).
CONCLUSION Routine fetal weight assessment at the 20 week anatomy scan can identify pregnancies that have an increased likelihood of being SGA in the third trimester and require a more intensive level of surveillance.
METHODS We analysed data from the 7 NHS trusts in the GAP programme that recorded their anatomy scans routinely. We included all singleton pregnancies from June 2024 to December 2025 that had a subsequent scan between 24+0 and 32+0 weeks gestation, and assessed the second trimester scan’s ability to predict SGA (<10th centile) in the 3rd trimester and at birth. All centiles were calculated using the GROW standard without sex adjustment, and we determined positive predictive value (PPV) and relative risk with 95% Confidence Interval (RR, CI)
RESULTS There were 8438 pregnancies in the 7 units over the study period with a scan EFW at anatomy scan at a median of 20+1 weeks. 211 (2.5%) fetuses were SGA, of which 177 (83.9%) were followed up with a scan at an average of 28+2 weeks. 65 of these fetuses were also SGA at the follow up scan (PPV: 36.7%, RR: 7.1 CI: 5.7-9.0). For SGA at birth (median gestational age 38+4 weeks), the PPV of SGA at anatomy scan was 31.6% (RR: 2.4; CI 1.9-3.1).
CONCLUSION Routine fetal weight assessment at the 20 week anatomy scan can identify pregnancies that have an increased likelihood of being SGA in the third trimester and require a more intensive level of surveillance.
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