Preterm preeclampsia as an independent risk factor for thromboembolism in a large national cohort.

Background: Preterm preeclampsia, a product of vascular dysfunction, is associated with prolonged hospital admission and proteinuria, significant risk factors for thromboembolism in pregnancy. The risk of thromboembolism in preterm preeclampsia warrants further investigation.

Objective: To determine the relationship between preterm preeclampsia and thromboembolic risk. We hypothesize that preterm preeclampsia is an independent risk factor for thromboembolism in pregnancy.

Study design: This is a retrospective cohort study using the National Inpatient Sample database via Healthcare Cost and Utilization Project-Agency for Healthcare Cost and Utilization Project from 2017-2019. All subjects with an International Classification of Diseases, Tenth Revision code for pregnancy or peripartum encounter were included. Subjects were excluded if the gestational age at delivery was <20 weeks or if they had a history of thromboembolism, inherited thrombophilia, or antiphospholipid syndrome. Patients with preterm (delivered <37 weeks) preeclampsia and term (delivered ≥37 weeks) preeclampsia were compared with those without preeclampsia. The primary outcome was a composite of any thromboembolic event, including pulmonary embolism, deep vein thrombosis, cerebral thrombosis or transient ischemic attack, or other thromboses. The secondary outcomes were rates of each type of thromboembolic event. The groups were compared via variance analysis, chi-square, and logistic regression analyses. The logistic regression included those variables that differed between groups with P<.05.

Results: Of individuals in the database, >2.2 million met the inclusion criteria. A total of 56,446 (2.7%) had preterm preeclampsia, and 86,152 (6.7%) had term preeclampsia. Those with preterm preeclampsia were more likely to be older, identify as non-Hispanic black, have obesity, have chronic hypertension among other chronic diseases, and be in the lowest quartile of income (P<.001). Among patients with preterm preeclampsia, 0.32% experienced thromboembolism, whereas those with term preeclampsia and without preeclampsia experienced thromboembolism at 0.10% and 0.09%, respectively. After controlling for confounders that differed between groups with P<.05, preterm preeclampsia remained independently associated with any thromboembolic event (adjusted odds ratio, 2.21 [95% confidence interval, 1.84-2.65]), and each type of thromboembolism. Term preeclampsia was not associated with an increased risk of thromboembolism (adjusted odds ratio, 1.18 [95% confidence interval, 0.94-1.48]).

Conclusion: Preterm preeclampsia is independently associated with an increased risk of thromboembolic events.