The Association Between Maternal Smoking During Pregnancy and Neonatal Intensive Care Unit Admission Among Full-Term Infants: A Finnish National Cohort Study

Purpose: Maternal smoking during pregnancy (SDP) is associated with adverse neonatal outcomes, but the specific conditions contributing to morbidity among term infants are poorly characterized. We examined whether maternal SDP increases the risk of neonatal intensive care unit (NICU) admission and antibiotic treatment during the first week of life, and identified NICU diagnoses more common among exposed infants. Methods: This register-based cohort study included all full-term (≥ 37+0 weeks’ gestation) singleton births in Finland from 2006 to 2018, using data from the Finnish Medical Birth Register and Hospital Discharge Register (n = 795,836; 95.2% of singleton births). Maternal smoking was categorized as no smoking, quit smoking during the first trimester (early smoking), or continued smoking after the first trimester. Primary outcomes were NICU admission and antibiotic treatment during the first week of life. Secondary outcomes included neonatal diagnoses and perinatal mortality. Stillbirths and early neonatal deaths were excluded from the analyses of treatments and diagnoses. Adjusted odds ratios (aORs) were estimated using logistic regression, adjusting for maternal age, parity, prepregnancy BMI, mode of delivery, and year of delivery. Results: Continued smoking was associated with increased odds of NICU admission (aOR 1.43) and antibiotic treatment (aOR 1.22), while early smoking was associated with more modest increases (aORs 1.17 and 1.19, respectively), compared with no exposure. Both smoking exposures were associated with an increased risk of bacterial sepsis or congenital pneumonia. Neonatal hypoglycemia was increased only with continued smoking. Continued smoking was also associated with an increased the risk stillbirth (aOR, 1.49) whereas early smoking was not associated with perinatal mortality. Conclusion: Maternal smoking during pregnancy was associated with an increased risk of infections and metabolic disturbances requiring intensive care among term infants. Continued smoking also increased the risk of stillbirth. These findings further support the importance of smoking cessation during pregnancy. Keywords: smoking, NICU, newborn, infection, hypoglycemia