Customised growth charts in large-for-gestational-age infants and the association with emergency caesarean section rate.

Background and Aim Large-for-gestational-age (LGA) infants are at increased risk of intrapartum complications. However, some infants classified as LGA may be appropriate-for-gestational-age (AGA) if adjusted for maternal stature. We determined whether customisation of birthweight centiles by maternal height, or height and weight, improves the detection of LGA infants at risk of complications. Methods We conducted a retrospective analysis of 38 246 term, singleton nulliparous women. We compared population birthweight centiles to those customised by height, or height and weight for complications including intrapartum caesarean section, instrumental delivery, postpartum haemorrhage, anal sphincter injury and neonatal outcomes. Results Those considered LGA when customised for height but AGA by population centiles (LGA-ht-only) were at increased risk of intrapartum emergency caesarean section compared with infants AGA on all charts (AGA-all); odds ratio (OR) 4.64, 95% CI 3.22-6.76. In contrast, infants considered LGA on population charts, but AGA when customised by height (LGA-pop-only) were not at increased risk compared to the AGA-all group (OR 1.43, 95% CI 0.70-1.88). Infants classified as LGA-ht-only compared to LGA-pop-only remained at significantly higher risk after adjustment for potential confounders (aOR 3.27; 95% CI 2.02-5.31). No difference was seen for any other outcomes. No benefit was seen with customisation by both maternal height and weight. Conclusion Women with an infant classified as AGA on population centiles but LGA when customised for height are at increased risk of intrapartum caesarean section. This is a population unrecognised in current practice. Fetal growth should be customised for maternal height when making assessments regarding the LGA infant.