The Impact of the Gestational Week on Perinatal Outcome in Newborns with Moderate Small for Gestational Age: A Retrospective Study

Abstract

Objective: Our study wants to assess the outcome of moderate small for gestational age (SGA) infants at term with reference to the week they find themselves in at birth in uncomplicated pregnancies. Material and Methods: The database is made of women delivering in Switzerland from 2005 through 2017 selecting uncomplicated singleton pregnancies in cephalic presentation, with birthweight between the 5th and 10th percentiles, and a gestational age at delivery between 37 0/7 and 41 6/7 weeks. We considered poor perinatal outcomes as either umbilical cord arterial pH<7.15, 5'Apgar score <7, admission to the neonatal intensive care unit, and/or perinatal mortality. Statistical analyses were performed using contingency tests and Spearman rank correlation adopting a p<0.05 as significant. Results: Out of the 429,863 available deliveries, we identifyied 1,796 cases matching our criteria. The final sample includes 1,327 (73.9%) vaginal deliveries and 473 (26.1%) caesarean sections (CS) and it is worth mentioning that the rate of secondary CS (r=0.828; p=0.03) and vaginal deliveries (r=0.965; p=0.01) increased with advancing gestation. In addition, 306 (19.3%) patients had induced labours. This is particularly concentrated between 40 and 41 weeks of gestation (r=0.967; p=0.002); among them, 80% delivered vaginally and 20% with a secondary CS. The percentage of adverse outcome was 16.9%, 11.3%, 8.6%, 18.8%, and 21.7% for gestational week 37, 38, 39, 41 and 42, respectively, whereas only 3 cases (0.17%) of intrauterine death occurred. Conclusion: Moderate SGA infants are best delivered between 39 0/7 and 40 0/7 weeks of gestation.