Extreme Preterm Delivery Between 24+0 and 27+6 Weeks: Factors Affecting Perinatal Outcome

<b>Objectives:</b> The aim of this study was to investigate the factors associated with the prediction of perinatal survival in pregnancies with extreme preterm delivery between 24⁺⁰ and 27⁺⁶ weeks' gestation. <b>Methods:</b> This screening cohort study was undertaken at a large tertiary obstetric and neonatal unit in the United Kingdom. We included singleton pregnancies that booked and delivered at our hospital. Logistic regression analysis was carried out to determine risks of complications in pregnancies delivering preterm after adjusting for maternal and pregnancy characteristics. Effect sizes were expressed as absolute risks (ARs) and odds ratios (ORs) (95% confidence intervals [CI]). <b>Results:</b> The study population included 53,649 singleton pregnancies, including 139 (0.3%) with preterm delivery between 24⁺⁰ and 27⁺⁶ weeks and 47,006 (99.7%) with term delivery ≥37 weeks. Multivariate regression analysis demonstrated that there was a significant contribution of uterine artery pulsatility index (UtA-PI) and cervical length, but not of maternal factors, in the prediction of preterm delivery <28 weeks. The risk of neonatal death and intact neurological survival in pregnancies delivering <28 weeks was 11.5% and 79.1%, respectively. Caesarean compared to vaginal delivery and female compared to male neonates were associated with a lower incidence of neurological morbidity (6.1% vs. 19.3%; <i>p</i> = 0.016 and 13.1% vs. 26.9%; <i>p</i> = 0.036, respectively). In the prediction of intact perinatal survival, the only significant variable was gestational age at delivery, with survival rates of about 50%, 65%, 80% and 90% at 24, 25, 26 and 27 weeks, respectively. <b>Conclusions:</b> In pregnancies with extreme preterm delivery between 24⁺⁰ and 27⁺⁶ weeks, caesarean compared to vaginal delivery and female compared to male neonates are associated with a lower incidence of neurological morbidity. The only significant factor in the prediction of intact perinatal survival is gestational age at delivery.