Neonatal outcome in macrosomia and gestational diabetes mellitus depending on the definition of macrosomia: a retrospective cohort study

Introduction Gestational diabetes increases the risk of neonatal macrosomia, which is associated with maternal and neonatal morbidity. However, the definition of macrosomia is inconsistent and includes both a fixed weight limit and a gestational age-dependent percentile. This study aimed to evaluate the association between different definitions of macrosomia and short-term neonatal outcome in pregnancies complicated by gestational diabetes. Material and methods In this retrospective single-center cohort study, 882 women with gestational diabetes and a singleton pregnancy were included. Adverse neonatal outcome was defined as 5-min Apgar score below eight and/or admission to the neonatal intensive care unit. We compared three different definitions of macrosomia: 1.) birthweight ≥ 4000 g, 2.) birthweight > 90th percentile, and 3.) length-related birthweight > 90th percentile. Eutrophic newborns served as controls and small-for-gestational-age infants were excluded. Additionally, umbilical artery Doppler parameters were explored. Results Overall, 220 out of 882 newborns (24.9%) met at least one definition of macrosomia: 129 (14.6%) with birthweight ≥ 4000 g, 126 (14.3%) with birthweight > 90th percentile, and 205 (23.2%) with length-related birthweight > 90th percentile. Short-term adverse neonatal outcome occurred in 6.2% ( n = 55). In the total cohort, macrosomia was not associated with adverse outcome. Newborns with a birthweight > 90th percentile showed a higher, but not statistically significant, rate of adverse outcome (odds ratio (OR) 1.5 [0.8–3.1], p = 0.231). In analyses restricted to macrosomic infants, those with birthweight > 90th percentile had higher rates of adverse outcome compared with those ≤ 90th percentile (8.7% vs. 1.1%; OR 8.9, 95% CI 1.1–70.2). This remained associated after adjustment for preterm birth (adjusted OR 8.8, 95% CI 1.1–71.4), although preterm birth was the strongest overall predictor. The effect was mainly observed in infants weighing < 4000 g. Umbilical artery Doppler showed limited predictive value. Conclusions Macrosomia represents a heterogeneous group not uniformly associated with adverse short-term neonatal outcome. Within this cohort, birthweight > 90th percentile, particularly in infants < 4000 g, was associated with higher rates of adverse outcome, whereas fixed weight thresholds were not. Gestational age–adjusted definitions may better identify at-risk neonates.