Background: The likelihood of recurrence of sudden infant death syndrome (SIDS) is an issue of biological, clinical, and legal interest. Obstetric complications are associated with an increased risk of SIDS and are likely to recur in subsequent pregnancies. We postulated that women whose infants died from SIDS would be more likely to have had obstetric complications in their other pregnancies.
Methods: We linked national UK databases of maternity-hospital discharges, perinatal deaths, and death certifications. We studied 258 096 women who had consecutive births in Scotland between 1985 and 2001.
Findings: Women who had an infant who died from SIDS were at increased risk in their next pregnancy of delivering an infant small for gestational age (odds ratio 2.27, 95% CI 1.54-3.34, p<0.0001) and of preterm birth (2.53, 1.82-3.53, p<0.0001). The risk of SIDS was higher for the children of women whose previous infant had been small for gestational age (1.87, 1.19-2.94, p=0.007) or preterm (1.93, 1.24-3.00, p=0.004). Multivariate analysis showed that all associations were explained by common maternal risk factors for SIDS and obstetric complications and by the likelihood of recurrence of fetal growth restriction and preterm birth.
Interpretation: Women whose infants die from SIDS are more likely to have complications in their other pregnancies. Recurrence of pregnancy complications predisposing to SIDS could partly explain why some women have recurrent SIDS.