Adverse perinatal outcomes in 665,244 term and post-term deliveries-a Norwegian population-based study

Objective: To assess the prevalence and risk of adverse perinatal outcomes in early-term (37⁺⁰-38⁺⁶ weeks), full-term (39⁺⁰-40⁺⁶ weeks), late-term (41⁺⁰-41⁺⁶ weeks), and post-term (>42⁺⁰ weeks) deliveries with spontaneous labor onset.

Study design: A population-based cohort with data from the Medical Birth Registry Norway (MBRN) and Statistics Norway (SSB) was conducted. The study population consisted of 665,244 women with cephalic singleton live births at term or post-term with spontaneous labor onset during the period of 1999-2014 in Norway. Maternal, obstetric, and fetal characteristics were obtained from the MBRN. Maternal education data were obtained from the SSB. The prevalence rates of adverse perinatal outcomes for each gestational age (GA) group were estimated. Inter-group differences were detected with Chi square tests. Multivariable regression analysis adjusted for maternal age, educational level, smoking, parity, maternal diabetes, and preeclampsia was used to assess adverse outcome prevalence for early- late-, and post-term births compared to full-term births.

Results: Deliveries at early-term were associated with an increased prevalence of neonatal jaundice, polyhydramnios, small for gestational age (SGA) status, respiratory support, and neonatal intensive care unit (NICU) admission compared with deliveries at GAs of 39-43 weeks (p < 0.001). Low 5-min Apgar scores and newborn antibiotic treatment occurred at an increased prevalence in both early-term and post-term infants, relative to the full-term group (p < 0.001). The prevalence of oligohydramnios, meconium-stained amniotic fluid, and newborn birth injuries increased with increasing GA.

Conclusions: More perinatal morbidity was observed among early-term infants compared to infants with later term deliveries, underscoring the need for cautious management of low-risk early-term deliveries.