Family history of VTE carries a dose-graded postpartum risk

Design

Nationwide population-based cohort, Swedish registers

Population

856,380 primiparous women without previous VTE, 1992 to 2018

Primary outcome

VTE within 90 days of delivery

Effect

Highest hereditary score HR 3.66 (95% CI 2.06 to 6.51) vs no family history

A Swedish nationwide cohort followed 856,380 first-time mothers without previous venous thromboembolism (VTE), delivering between 1992 and 2018, for VTE in the 90 days after birth. Family members were identified through the national multi-generation register, and a hereditary score weighted each affected relative by how closely related they were.

Overall 788 women (0.09%) had a postpartum VTE. An affected parent was associated with about double the risk (HR 2.03, 95% CI 1.60 to 2.56), and an affected full sibling with HR 2.55 (1.53 to 4.26). The risk rose step by step with the hereditary score: HR 1.50 in the lowest category, 2.89 in the middle and 3.66 (2.06 to 6.51) in the highest. Obesity, caesarean delivery, pre-eclampsia, postpartum haemorrhage with transfusion and infection also predicted VTE independently.

This matters because many postpartum risk tools treat family history as a yes-or-no item. The data suggest who is affected, and how many, adds information. It is an association study, so it says who is at higher risk, not that prophylaxis prevents events in that group.

In practice, take a fuller family history at booking and again at delivery, and weigh it with the other risk factors in your local thromboprophylaxis tool rather than in isolation. Your current guideline on postpartum prophylaxis has not changed on the strength of this study.

• Ask at booking which relatives had a VTE: parent, sibling, half-sibling, grandparent or cousin.
• Record the number of affected relatives, not just yes or no.
• An affected parent or full sibling was linked to about double to two-and-a-half times the postpartum risk.
• Combine family history with caesarean birth, obesity, pre-eclampsia and haemorrhage in your local risk score.
• Revisit the score after delivery, when new risk factors such as transfusion or infection may appear.

Why it matters

A yes-or-no family history box throws away information that grades risk.

Don't overread it

This was observational; it identifies higher-risk women but does not show that prophylaxis helps them.

The statistics, in plain English

A hazard ratio of 2.03 means the rate of postpartum VTE was about twice as high in women with an affected parent. Because the baseline rate was low (under 1 in 1,000), even a tripled risk leaves the absolute risk small for most women; the value lies in combining it with other risk factors.

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