Stillbirth risk in a second pregnancy.

OBJECTIVE: To estimate the risk of stillbirth in a second pregnancy when previous stillbirth, preterm, and small-for-gestational age (SGA) births occurred in the previous pregnancy.

METHODS: This was a population-based cohort study in New South Wales Australia from 2002 to 2006. Singleton births in a first pregnancy were linked to a second pregnancy using data from the New South Wales Midwives Data Collection and the New South Wales Perinatal Death Database. Deaths were classified according to the Perinatal Mortality Classifications of the Perinatal Society of Australia and New Zealand. Crude and adjusted hazard ratios were estimated using a proportional hazards model.

RESULTS: Delivery of an SGA newborn in the first pregnancy was associated with increased risks of stillbirth in a second pregnancy (hazard ratio 1.73, 95% confidence interval [CI] 1.15-2.60) and risk was further increased with prematurity (hazard ratio 5.65, 95% CI 1.76-18.12). Stillbirth in a first pregnancy had a nonsignificant association with stillbirth in the second pregnancy (hazard ratio 2.03, 95% CI 0.60-6.90). For women aged 30-34 years, the absolute risk of stillbirth up to 40 completed weeks of gestation was 4.84 per 1,000 among women whose first pregnancy was a stillbirth and 7.19 per 1,000 among women whose first pregnancy was preterm and SGA.

CONCLUSION: Delivering an SGA and preterm neonate in a first pregnancy is associated with greater risks for stillbirth in a second pregnancy than delivering a previous stillbirth. All factors merit improved surveillance in a subsequent pregnancy, and research should address underlying factors common to all three outcomes.