Prevalence, interactions, determinants and outcomes of low birth weight, small for gestational age and fetal growth restriction among term neonates

Abstract Introduction Small for gestational age and fetal growth restriction are two leading causes for low birth weight in term newborns. Due to the considerable overlap, the exact interactions between these groups have not been adequately studied. We aim to determine the prevalence, interactions, determinants, and outcomes of low birth weight, small for gestational age, and fetal growth restriction in term neonates. Methods A cross-sectional study with a short-term follow-up was conducted at Colombo North Teaching Hospital, Ragama, Sri Lanka, between June and August 2025. All neonates of singleton pregnancies born at term were eligible. Stillbirths, multiple pregnancies and newborns born preterm, post-term, with uncertain gestations or with antenatally diagnosed congenital anomalies were excluded. The prevalence and interactions of low birth weight, small for gestational age, and fetal growth restriction were determined, and their risk factors were analysed. Results 437 term newborns (male-54.0%, primipara-53.3%) were recruited. The prevalence of low birth weight, small for gestational age, and fetal growth restriction were 14.0%, 15.1% and 14.9%, respectively. Of the low birth weight neonates, 75.4% were small for gestational age, and 50.8% had fetal growth restriction, while 20% did not have either. Of the low birth weight neonates who were small for gestational age, 18 did not have fetal growth restriction, indicating 29.5% of low birth weight neonates were constitutionally small. Female sex of the baby, low paternal education level, and pregnancy induced hypertension in the mother were significant independent risk factors for low birth weight. Low birth weight and fetal growth restriction were associated with a higher incidence of intensive care admissions, neonatal sepsis, and neonatal jaundice. Conclusion The prevalence of low birth weight, small for gestational age, and fetal growth restriction in term neonates was 14.0%, 15.1% and 14.9%, respectively. Among low birth weight neonates, one-fifth had neither small for gestational age nor fetal growth restriction; therefore, healthy. An additional 30% of low birth weight babies did not have fetal growth restriction, indicating they are constitutionally small. Neonatal complications were associated more with low birth weight and fetal growth restriction than with small for gestational age.