Neonatal Morbidities in Infants Born Late Preterm at 35-36 Weeks of Gestation

Preterm infants, born at 35-36 weeks, are often admitted to a level I unit (well-newborn maternity wards). However, they may still be physiologically immature.

Infants born late preterm have a higher risk of neonatal mortality than their term (37-41 weeks) counterparts. Additionally, they also have a higher risk of neonatal morbidity, with an increased health care burden. This risk in infants born at 35-36 weeks compared with term infants is yet to be studied briefly on a national population level.

A recent study assessed the risk for neonatal morbidities among infants born late preterm at 35-36 gestational weeks, early term (37-38 weeks), and late-term (41 weeks) infants, compared with full-term (39-40 weeks) infants.

This nationwide population-based cohort study was carried out in 1,650,450 non-malformed liveborn singleton infants born at 35-41 weeks between 1998 and 2016 in Sweden. The relative risks for low Apgar score (0-3) at 5 minutes; respiratory, metabolic, infectious, and neurologic morbidities; and severe neonatal morbidity (composite outcome) were adjusted for maternal, pregnancy, delivery, and infant characteristics.

The results were as follows-

• Infants born at 35-36 weeks showed higher adjusted relative risks and proportions for metabolic morbidity, respiratory morbidity, severe neonatal morbidity, infectious morbidity, neurologic morbidity, and a low Apgar score, than the infants born at 39-40 weeks.
• The risks for respiratory, severe neonatal morbidity, infectious, neurologic morbidities, and low Apgar score were found to be greatest at 35 weeks, which slowly decreased until 39 weeks, and then further increased during 39-41 weeks.

Thus, infants born late preterm at 35-36 weeks of gestation possess a greater risk of neonatal morbidities, however, the absolute risks for severe neonatal morbidities are low. Hence there is a need of preventing late preterm delivery to decrease the burden of neonatal morbidity and help professionals and families with a better risk assessment.

Source: Mitha A, Chen R, Altman M, Johansson S, Stephansson O, Bolk J. Neonatal Morbidities in Infants Born Late Preterm at 35-36 Weeks of Gestation: A Swedish Nationwide Population-based Study. The Journal of Pediatrics. 2021;233:43-50. DOI:https://doi.org/10.1016/j.jpeds.2021.02.066