Association Between Newborn Birthweight 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 birthweight 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 using selected ICD-9-CM codes. Controls were randomly selected postpartum women without VTE, matched on birth year. Birthweight 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 birthweights (<2500g and >4000g, respectively) versus mothers of newborns of normal birthweight (2500-4000g). Logistic regression models adjusted for maternal age, race, education, BMI, parity, delivery methods, gestational length, smoking, gestational diabetes and pre-eclampsia. Cases (n=547) were older, had a higher BMI, and experienced more pregnancy-related complications than controls (n=9482). Compared with mothers of newborns of normal birth weight, mothers of low birthweight newborns had a 3-fold increased risk of VTE, which persisted after multivariable adjustment (OR 2.98, 95%CI 1.80-4.93). Mothers of high birthweight newborns had only a slightly increased risk of VTE, which was attenuated after multivariable adjustment (OR 1.26, 95%CI 0.99-1.61).
Conclusions—The delivery of a low birthweight newborn is associated with a 3-fold increased risk of maternal postpartum VTE. This should be considered when assessing VTE risk at delivery.
- Received August 12, 2014.
- Revision received January 3, 2015.
- Accepted February 13, 2015.