Objective: To assess inherited predisposition to spontaneous preterm delivery.
Methods: In this retrospective cohort study, intergenerational data on deliveries in mother-daughter pairs were analyzed from the Aberdeen Maternity Neonatal Databank using multilevel logistic regression. The study included an exposed cohort of all women born spontaneously preterm or whose mothers had experienced at least one spontaneous preterm delivery (at 24-37 weeks of gestation). The unexposed cohort included women who were born at term (after 37 weeks of gestation) or those whose mothers had never experienced any spontaneous preterm deliveries (24-37 weeks of gestation). The primary outcome was spontaneous preterm delivery in the daughters' pregnancies. Results are shown as adjusted odds ratios (ORs) and 95% confidence intervals (CIs).
Results: We identified 22,343 pregnancies occurring in 13,845 daughters born to 11,576 mothers. Women who were born spontaneously preterm had significantly higher odds of delivering preterm babies (OR 1.49, 95% CI 1.12-1.99). A stronger association was seen when the analysis was restricted to nulliparous women who had been born spontaneously preterm (OR 1.60, 95% CI 1.16-2.21). Other predictors of a woman having a spontaneous preterm delivery were age at delivery younger than 20 years (OR 1.67, 95% CI 1.43-1.94), lower socioeconomic status (OR 1.22, 95% CI 1.04-1.44), smoking more than 10 cigarettes per day (OR 1.47, 95% CI 1.27-1.71), body mass index 19 kg/m or less (OR 1.48, 95% CI 1.24-1.77), previous preterm delivery (OR 2.51, 95% CI 1.71-3.66). The risk of a woman delivering spontaneously preterm was increased even if her mother had a history of spontaneous preterm delivery in any other pregnancy (OR 1.35, 95% CI 1.12-1.63). The absolute risk of spontaneously delivering preterm in women who were born preterm was 9% as opposed to 6.2% in those who were born full-term. This gives an increase in risk of spontaneous preterm birth of 2.8% in women who were born spontaneously preterm.
Conclusion: Women born spontaneously preterm or with siblings delivered in a similar manner have an increased risk of spontaneous preterm delivery in their own pregnancies.
Level of evidence: II.