Risk of short-term cardiovascular disease in relation to the mode of delivery in singleton pregnancies: a retrospective cohort study.

Background: Cardiovascular disease (CVD) is increasing in prevalence and affects up to 4% of pregnancies in otherwise healthy persons. The specific factors that drive the development of CVD in pregnant people are poorly characterised. This study aimed to determine whether the mode of delivery in singletons affects the risk of cardiovascular morbidity and mortality within one year in patients without prior CVD.

Methods: We designed a retrospective cohort study utilising the Nationwide Readmissions Database (NRD) to identify singleton delivery hospitalisations in the United States from Jan 1, 2010 to Nov 30, 2018. International Classification of Disease (ICD) versions 9 and 10 codes were used to identify patients with readmission for CVD within the calendar year of index delivery. Patients aged 15-54 who underwent a singleton vaginal or caesarean delivery were included. Patients with pre-existing CVD hospitalisations before or during delivery, ectopic pregnancies, or abortive outcomes were excluded. Participant data was retrieved from the NRD database. The primary outcome was hospital readmission, defined by ICD 9 and 10 codes for fatal or non-fatal CVD in the same calendar year as delivery. Cox proportional hazard regression models were used to adjust for confounders. These included maternal age, hospital bed size, hospital type, hospital teaching status, income quartile, insurance, and year of delivery. Additional sub-analyses were performed adjusting for hypertensive disorders of pregnancy and diabetes mellitus.

Findings: Of the 14,179,299 singleton deliveries, 32% (n = 4,553,492) underwent a caesarean. CVD readmissions occurred in 255.2 per 100,000 (n = 11,710) caesarean deliveries compared with 133.9 per 100,000 (n = 12,507) vaginal deliveries (rate difference [RD], 121.4, 95% confidence interval [CI], 114.8-127.9; hazard ratio [HR] adjusted for all confounders including hypertensive disorders of pregnancy and diabetes mellitus was 1.42, 95% CI 1.35-1.50). This association was highest in the first 0-29 days following delivery (HR 1.68, 95% CI 1.59-1.78). The risk of readmission for CVD persisted for one year.

Interpretation: These findings suggest that caesarean delivery of singletons is associated with a higher risk of cardiovascular morbidity in patients without pre-existing CVD. This risk was highest in the first month but remained elevated for one year after delivery. These findings add to the accumulating evidence that undergoing caesarean delivery may have long-standing health implications and support the extension of the post-partum surveillance period. Limitations of this study include the lack of adjustment for body mass index, race, and parity. We were also unable to determine the reason for the caesarean delivery.

Funding: None.