Interpretation
The results of our analyses have immediate clinical utility for antenatal surveillance of fetal growth. Firstly, the 11th centile as a threshold for the whole population, regardless of risk assessment, confirms that the conventional 10th centile for SGA remains a useful general standard. The 15th centile as best cut-off to assess stillbirth risk in a low risk population (Figure 2) is a new finding and may be a useful limit for fundal height measurements but requires further investigation. A similar cut-off has been proposed for the assessment of risk of neonatal death 32.
Secondly, the observed optimal threshold of the 2.7thcentile in high risk pregnancies would confirm the 3rdcentile line as an appropriate cut-off to indicate the presence of fetal growth restriction, as proposed in the NHS England guidelines33 and the new GAP care pathway 34. The recommendation is that a fetus with a weight below 3rd centile should be considered for delivery by 37 weeks, regardless of the results of umbilical artery Doppler investigation because of its limited effectiveness for the assessment of growth status late in third trimester 9. Fetuses with a weight between the 3rd and 10thcentile are also at risk, but delivery can be delayed until 39 weeks if Doppler indices more suitable for assessment at term (uterine artery and middle cerebral artery) remain normal. 9,33,34