FM04 INTERGROWTH-21st symphysis-fundal height chart: safe for use in the NHS?
Fetal Medicine
Information
INTRODUCTION NHS England recently issued a directive 1 against use of the INTERGROWTH 21st (IG21) estimated fetal weight standard because of its low antenatal screen positive rate for small for gestational age (SGA)2. We wanted to investigate whether INTERGROWTH’s standard for symphysis-fundal height3, based on the same 8-country cohort as their fetal weight standard, has an appropriate screen positive rate when applied in the NHS population.
METHODS We studied 90,601 consecutive low risk pregnancies from 43 NHS Trusts between 2023 and 2025 that had 3 or more third trimester SFH measurements. One measurement was selected randomly from each pregnancy and the IG21 SFH standard3 and the GROW 2.0 SFH standard4 were applied to compare SGA (<10th centile) screen positive rates.
RESULTS The Table lists pregnancy characteristics for our cohort and compares them with those reported for the IG21 standard2. Mothers in the NHS cohort were taller, heavier, with higher BMI and parity, and had babies with lower prematurity rate and higher term birthweight. The fundal height measurements were at a median 33+6 weeks (IQR 29+5–36+3). 7939 (8.8%) of SFH measurements were SGA according to GROW and 4593 (5.1%) according to IG21, a reduction of screen positive rate by 42%.
CONCLUSION Compared to the NHS population, the IG21 SFH standard is derived from pregnancies of smaller mothers and lower birthweights at term. As a result, it has a much lower screen positive SGA rate and is likely to miss many pregnancies potentially at risk due to fetal growth restriction.
METHODS We studied 90,601 consecutive low risk pregnancies from 43 NHS Trusts between 2023 and 2025 that had 3 or more third trimester SFH measurements. One measurement was selected randomly from each pregnancy and the IG21 SFH standard3 and the GROW 2.0 SFH standard4 were applied to compare SGA (<10th centile) screen positive rates.
RESULTS The Table lists pregnancy characteristics for our cohort and compares them with those reported for the IG21 standard2. Mothers in the NHS cohort were taller, heavier, with higher BMI and parity, and had babies with lower prematurity rate and higher term birthweight. The fundal height measurements were at a median 33+6 weeks (IQR 29+5–36+3). 7939 (8.8%) of SFH measurements were SGA according to GROW and 4593 (5.1%) according to IG21, a reduction of screen positive rate by 42%.
CONCLUSION Compared to the NHS population, the IG21 SFH standard is derived from pregnancies of smaller mothers and lower birthweights at term. As a result, it has a much lower screen positive SGA rate and is likely to miss many pregnancies potentially at risk due to fetal growth restriction.
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Friday 27th March