Risk factors for venous thromboembolism after birth - a nationwide study

Abstract

Purpose: The risk of venous thromboembolism (VTE) is increased during pregnancy and 6 weeks following childbirth. We examined risk factors for VTE following childbirth with focus on mode of birth, obesity, and age. Method(s): Individual-level linkage of nationwide administrative registers was used. All women were included at the time of first birth during 2003-2011 and followed for six weeks. The risk of VTE (including deep venous thrombosis and pulmonary embolism) was investigated using a multivariable Cox regression including maternal age (at birth), pre-pregnancy body mass index (BMI), smoking (during pregnancy), previous VTE, and mode of delivery. Result(s): A total of 299,294 women were included of which 109 (0.04%) experienced a VTE. Multivariable Cox regression analysis revealed (Figure 1) that maternal age above 35 years increased the risk with a hazard ratio (HR) 2.2 (95% confidence interval [CI] 1.4-3.6) compared to women 20-30 years old. Overweight (25 <30) and obesity (BMI>=30) increased the risk by HR 2.0 (CI 1.3-3.1) and 2.9 (CI 1.8-4.6), respectively, compared to normal weight women (18.5 <25). Previous VTE increased the risk substantially HR 51.2 (CI 29.4-89.3), whereas smoking was insignificant. Caesarean section was grouped in 4 depending on time of caesarean section (before onset of labour/during labour) and acute/elective. Only acute caesarean section before labour increased the risk of VTE significantly by HR 3.5 (CI 1.9-6.3) compared to vaginal delivery. (Figure presented) Conclusion(s): In a large nationwide cohort of fertile women, acute caesarean section before labour, maternal age >35 years, and being overweight or obese were associated with an increased VTE risk following childbirth. Focus on risk stratification of pregnant women might help identify women at higher risk of VTE after birth.