Preterm delivery, smoking predict pregnancy-related venous thromboembolism

Smoking and preterm delivery, along with ethnicity, blood type, and mode of delivery, are strong predictors of pregnancy-associated venous thromboembolism (VTE), according to a recent Singapore study.

“The risk of developing VTE extends throughout all three trimesters and beyond delivery to the six weeks postpartum,” researchers said. “Screening using a VTE risk assessment tool to identify high-risk women who would benefit from thromboprophylaxis should therefore be conducted early in pregnancy and again just after delivery.”

Eighty-nine patients with confirmed pregnancy-associated VTE were enrolled and compared against 926 non-VTE controls. Most of the cases were deep vein thrombosis (DVT; n=71); only 18 pulmonary embolism (PE) cases were reported. Twenty-nine episodes of VTE occurred postpartum and 60 were recorded during the antepartum period. [J Perinat Med 2020;doi:10.1515/jpm-2020-0298]

Multivariable logistic regression analysis was performed to identify risk factors for VTE in pregnancy. Smokers, for example, were more than five times as likely as nonsmokers to develop the condition (odds ratio [OR], 5.44, 95 percent confidence interval [CI], 2.12–14.00; p=0.0002). The same was true for preterm delivery (OR, 5.06, 95 percent CI, 1.25–20.51; p=0.023).

In addition, those who were of non-O blood type saw a significant increase in the risk of pregnancy-associated VTE (OR, 3.19, 95 percent CI, 1.67–6.11; p=0.0005), as did women who were of Malay ethnicity (OR, 1.81, 95 percent CI, 1.01–3.26; p=0.048).

Caesarean delivery was likewise detected as a strong risk factor for pregnancy-associated VTE (OR, 3.58, 95 percent CI, 1.07–12.02; p=0.04), as was having parity ≥3 (OR, 2.84, 95 percent CI, 1.16–6.97; p=0.023). The statistical analysis was adjusted for potential confounders, including age, body mass index, infant low birth weight, and postpartum haemorrhage.

“VTE, which includes DVT and PE, is 4–6 times more common in pregnant women compared to age-matched nonpregnant women,” researchers said. [Ann Intern Med 2005;143:697–706; Br J Haematol 2012;156:366–73]

Notably, ethnicity and blood type were emergent and easily identifiable correlates that could potentially help boost the current risk assessment models. Weight gain, another potential risk factor, was not studied. The small sample size and the static measurement of body mass index are among the study limitations that could have led to under-detection of other risk factors.

In addition, caesarean delivery as a strong risk factor for postpartum VTE is of particular interest to Singapore, where the prevalence of this mode of delivery has been on the rise, researchers said.

“This study offers a perspective on the burden of pregnancy-associated VTE in a Singaporean context, and should serve to inform policies regarding VTE thromboprophylaxis,” they added.