Association Between Newborn Birth Weight and the Risk of Postpartum Maternal Venous Thromboembolism A Population-Based Case-Control Study

Background-Postpartum venous thromboembolism (VTE) is a potentially fatal and preventable event leading to substantial short-and long-term morbidity. We sought to evaluate whether the delivery of term newborns of low or high birth weight was associated with greater risks of VTE. Methods and Results-In a population-based case-control study conducted in Washington State from 1987 through 2011, cases of hospitalized VTE within 3 months of delivery were identified by using selected International Classification of Diseases, Ninth Revision, Clinical Modification codes. Controls were randomly selected postpartum women without VTE, matched on birth year. Birth weight and other maternal and pregnancy characteristics were extracted from birth certificate data. Among term live singleton deliveries, we compared the risk of VTE for mothers of newborns of low and high birth weights (<2500 g and >4000 g, respectively) versus mothers of newborns of normal birth weight (25004000 g). Logistic regression models were adjusted for maternal age, race, education, body mass index, parity, delivery methods, gestational length, smoking, gestational diabetes mellitus, and preeclampsia. Patients with VTE (n=547) were older, had a higher body mass index, and experienced more pregnancy-related complications than controls (n=9482). In comparison with mothers of newborns with normal birth weight, mothers of newborns with low birth weight had a 3-fold increased risk of VTE, which persisted after multivariable adjustment (odds ratio, 2.98; 95% confidence interval, 1.80-4.93). Mothers of newborns with high birth weight had only a slightly increased risk of VTE, which was attenuated after multivariable adjustment (odds ratio, 1.26; 95% confidence interval, 0.99-1.61). Conclusions-The delivery of a newborn with low birth weight is associated with a 3-fold increased risk of maternal postpartum VTE. This should be considered when assessing VTE risk at delivery.