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Jonathan Douxfils: Navigating the VTE Risk Continuum in Reproductive Medicine

Jonathan Douxfils/LinkedIn

Sep 29, 2026, 16:35

Jonathan Douxfils: Navigating the VTE Risk Continuum in Reproductive Medicine

Jonathan Douxfils, Director of the Research Unit in Clinical Pharmacology and Toxicology at University of Namur, shared a post on LinkedIn:

“I was pleased to participate in the FFER meeting in Montpellier, where I presented on VTE risk from assistedreproduction to postpartum.

The key message: thrombotic risk in reproductive medicine is not a single event, but a continuum:

ART – pregnancy – delivery – postpartum – contraception restart.

Although VTE remains uncommon in absolute terms, the burden is clinically relevant:

In the general obstetric population, VTE occurs in 1.2–1.4 per 1,000 pregnancies, with >50% of events occurring after delivery.
Pregnancy increases VTE risk 4–5-fold, while the early postpartum period can increase it up to 60-fold compared with non-pregnant women.
The first postpartum weeks are critical: around 9 VTE events per 10,000 deliveries in week 1, decreasing to 1 per 10,000 by week 4.
ART adds a specific early risk window. In IVF pregnancies, first-trimester VTE risk is increased, particularly after fresh embryo transfer. OHSS remains the major red flag, with an absolute VTE risk reported around 1.7%.
But ART alone is not an indication for systematic anticoagulation. The clinical challenge is to identify who accumulates risk: previous VTE, OHSS, fresh transfer, multiple pregnancy, caesarean section, pre-eclampsia, obesity, infection or postpartum haemorrhage.

Another important point: estrogens are not interchangeable. Ethinylestradiol, and Natural Estrogens like E2 and E4 differ in hepatic impact, thrombin generation, APC resistance and expected thrombotic profile.

Why does this matter?

In programmed frozen embryo transfer, E2 is used to prepare the endometrium, but oral estrogen substitution can modify thrombin generation and fibrinolysis.

E4 may offer a pharmacologically attractive alternative because of its lower hepatic impact and more neutral haemostatic profile.

However, replacing E2 by E4 would first require dedicated ART studies showing preserved endometrial receptivity, pregnancy outcomes and improved haemostatic markers.

For now: a research priority, not a clinical recommendation.

Many thanks to the FFER organisers and Gedeon Richter France for the invitation and the excellent discussions.”

Jonathan Douxfils