Impact of obstetric factors on outcome of extremely preterm births in Sweden: prospective population-based observational study (EXPRESS)

Abstract

Introduction: A population-based observational study investigated the contribution of obstetric factors to the survival and postnatal development of extremely preterm infants.

Material and methods: Mortality up to 1 year and neurodevelopment at 2.5 years (Bayley-III test, cerebral palsy, vision, hearing) were evaluated in infants born before 27 weeks of gestation in Sweden 2004-2007 (n = 1011), using logistic regression analyses of risk factors.

Results: Of 844 fetuses alive at admission, 8.4% died in utero before labor, 7.8% died intrapartum. Of 707 live-born infants, 15% died within 24 h, 70% survived ≥365 days, 64% were assessed at 2.5 years. The risk of death within 24 h after birth decreased with gestational age [odds ratio (OR) 0.3; 95% CI 0.2-0.4], antenatal corticosteroids (OR 0.3; 95% CI 0.1-0.6), and cesarean section (OR 0.4; 95% CI 0.2-0.9); it increased with multiple birth (OR 3.0; 95% CI 1.5-6.0), vaginal breech delivery (OR 2.3; 95% CI 1.0-5.1), 5-min Apgar score <4 (OR 50.4; 95% CI 28.2-90.2), and birth at a level II hospital (OR 2.6; 95% CI 1.2-5.3). The risk of death between 1 and 365 days remained significantly decreased for gestational age and corticosteroids. The risk of mental developmental delay at 2.5 years decreased with gestational age, birthweight and fetal growth; it increased with vaginal breech delivery (OR 2.0; 95% CI 1.2-7.4), male gender, low Apgar score and high Clinical Risk Index for Babies score.

Conclusion: Several obstetric factors, including abdominal delivery, influenced the risk of death within the first day of life, but not later. Antenatal corticosteroids and gestational age decreased the mortality up to 1 year. Mental developmental delay was related to vaginal breech delivery.

Keywords: Extremely preterm birth; breech delivery; cesarean section; mortality; neurodevelopmental outcome; obstetric interventions; risk factors.