The study purpose was to assess the relationship between various grades of preterm birth (moderate preterm: 33-36 weeks; severe preterm: 27-32 weeks; extreme preterm: ≤ 26 weeks) in the first pregnancy and neonatal mortality (death within 28 days of birth; early: 0-7 days; late: 8-28 days) in the second pregnancy. Using the Missouri maternally-linked dataset (1989-2005), a population-based, retrospective cohort analysis with propensity score-weighted matching was conducted on mothers with two consecutive singleton live births (n = 310,653 women). Women with a prior preterm birth were more likely to subsequently experience neonatal death. The odds increased in a dose-dependent pattern with ascending severity of the preterm event in the first pregnancy (moderate preterm: AOR = 1.32; 95% CI: 1.10-1.60; severe preterm: AOR = 2.62; 95% CI: 2.01-3.41; extreme preterm: AOR = 5.84; 95% CI: 4.28-7.97; p value for trend < 0.001). However, the pathway for the relationship between prior preterm birth and subsequent neonatal mortality may be the recurrence of preterm birth.
Keywords: Birth outcomes; neonatal mortality; pregnancy; preterm birth.