Maternal risk of ischaemic heart disease following elective and spontaneous pre-term delivery: retrospective cohort study of 750 350 singleton pregnancies

BACKGROUND: Previous studies have demonstrated an overall association between pre-term delivery and maternal risk of subsequent ischaemic heart disease (IHD). The underlying mechanism is unknown. We explored whether the association was specific to spontaneous or elective pre-term delivery. METHODS: We linked three Scottish routine data sources. The Scottish Morbidity Record 1 collects data on all acute hospital admissions, Scottish Morbidity Record 2 collects data on all pregnancies and Scotland's Registrar General collates data from all death certificates. Cox proportional hazards models were used to explore associations between pre-term delivery and subsequent IHD events (fatal and non-fatal) and IHD deaths. Analysis was restricted to women aged between 35 and 65 years at either the time of their first IHD event or at the end of follow-up. RESULTS: The cohort comprised 750,350 women who delivered a live, singleton infant following their first pregnancy. We demonstrated independent associations between pre-term delivery and IHD death [hazards ratio (HR) 2.26, 95% confidence interval (CI) 1.88-2.71] and total IHD events (HR 1.58, 95% CI 1.47-1.71). Associations were greater for elective than spontaneous pre-term delivery (P = 0.005). There was a trend whereby the association between pre-term delivery and IHD increased with decreasing age at first event. CONCLUSIONS: We observed a stronger association between elective pre-term delivery and IHD, than spontaneous pre-term delivery and IHD. Elective pre-term delivery is usually undertaken because of growth restriction or pre-eclampsia, resulting from placental dysfunction. The age trend observed suggests an underlying genetic predisposition to both placental dysfunction and IHD.