Stillbirth or preterm birth linked to risk of blood clots

Stillbirth or preterm birth may dramatically increase a woman’s risk of developing a blood clot immediately postpartum, according to the results of a large, population-based study appearing on the website of Blood, the journal of the American Society of Hematology (ASH).

The UK researchers who conducted the study found that venous thromboembolism (VTE) risk varies modestly by recognized factors during the antepartum period. However, they found that women who had experienced stillbirths, preterm births, obstetric hemorrhage, caesarean delivery, medical co-morbidities, or had a body mass index ≥30kg/m² were at much higher risk of VTE following delivery.

The researchers reviewed data from more than 375,000 pregnancies in women aged 15 to 44 between January 1995 and July 2009.

The researchers discovered a significant correlation in the postpartum period between VTE risk and stillbirth (a 6-fold increased risk of VTE compared with women who did not have a stillbirth, IRR 6.2), a risk factor that is not currently addressed in VTE risk assessment guidelines. The researchers also determined other factors that led to an increased risk of VTE, including 3 or more previous births (IRR 2.07), preterm birth (prior to 37 weeks gestation, IRR 2.69), and obstetric hemorrhage (IRR 2.89). 

“Preventing VTE in pregnancy remains a challenging topic for clinicians since there is still disagreement as to which clinical, lifestyle, and socio-demographic factors qualify women as high-risk, and data are lacking about the relative impact of those factors on their risk of VTE,” said author Matthew Grainge, PhD, in an ASH press release. “Moreover, many studies have made the incorrect assumption that any risk factors identified have a similar impact on VTE rates in both pregnant women and new moms.”