Neonatal Morbidity of Small- and Large-for-Gestational-Age Neonates Born at Term in Uncomplicated Pregnancies

Abstract

Objective: To compare morbidity among small-for-gestational-age (SGA; birth weight less than the 10th percentile for gestational age), appropriate-for-gestational-age (AGA; birth weight 10th to 90th percentile; reference group), and large-for-gestational-age (LGA; birth weight greater than the 90th percentile) neonates in apparently uncomplicated pregnancies at term (37 weeks of gestation or greater).

Methods: This secondary analysis, derived from an observational obstetric cohort of 115,502 deliveries, included women with apparently uncomplicated pregnancies of nonanomalous singletons who had confirmatory ultrasound dating no later than the second trimester and who delivered between 37 0/7 and 42 6/7 weeks of gestation. We used two different composite neonatal morbidity outcomes: hypoxic composite neonatal morbidity for SGA and traumatic composite neonatal morbidity for LGA neonates. Log Poisson relative risks (RRs) with 95% CIs adjusted for potential confounding factors (nulliparity, body mass index, insurance status, and neonatal sex) were calculated.

Results: Among the 63,436 women who met our inclusion criteria, SGA occurred in 7.9% (n=4,983) and LGA in 8.3% (n=5,253). Hypoxic composite neonatal morbidity was significantly higher in SGA (1.1%) compared with AGA (0.7%; adjusted RR 1.44, 95% CI 1.07-1.93) but similar between LGA (0.6%) and AGA (adjusted RR 0.84, 95% CI 0.58-1.22). Traumatic composite neonatal morbidity was significantly higher in LGA (1.9%) than AGA (1.0%; adjusted RR 1.88, 95% CI 1.51-2.34) but similar in SGA (1.3%) compared with AGA (adjusted RR 1.28, 95% CI 0.98-1.67).

Conclusion: Among women with uncomplicated pregnancies, hypoxic composite neonatal morbidity is more common with SGA neonates and traumatic-composite neonatal morbidity is more common with LGA neonates.

Fig 1

Analysis cohort inclusion. APEX, Assessment of Perinatal Excellence. *Adequate pregnancy dating was defined as a pregnancy dated by last menstrual period and first- or second-trimester ultrasonogram, first- or second-trimester ultrasonogram alone, or assisted reproductive technology. ^†Categories not mutually exclusive. ^‡A pregnancy was considered complicated if the woman had any of the following: diabetes (pregestational or gestational), chronic hypertension, history of deep venous thrombus or pulmonary embolism, hypertensive disease of pregnancy (gestational hypertension or preeclampsia) with an onset before delivery hospital admission, thrombophilia excluding MTHFR, anticoagulant use, previa, or any of the following as a reason for delivery hospital admission: vaginal bleeding or abruption, deep venous thrombus, asthma exacerbation, seizures, or other nonobstetric maternal medical condition. In absence of these conditions, a woman was considered to have an uncomplicated pregnancy.