Grand Rounds

Embolism Following IVF: Does Fresh or Frozen-Thawed Transfer Matter?

BACKGROUND AND PURPOSE:

Olausson et al. (Journal of Thrombosis Haemostasis, 2020) compared the incidence of VTE and PE during the first trimester of IVF pregnancies using fresh or frozen-thawed embryo transfer to those of natural pregnancies

Population-based cohort study (1992 to 2012)
- National registries (Sweden) that covers 97% to 99.5% of all deliveries
Participants
- Nulliparous | Ages 15 to 50 years
Exposures
- IVF with fresh embryo transfer
- IVF with frozen-thawed embryo transfer
- Natural conception
Study design
- Authors calculated incidences of VTE and PE and estimated time-varying hazard ratio (HR) for all trimesters after fresh or frozen-thawed embryo transfer IVF compared to natural conception
Primary outcome
- Venous thromboembolism and pulmonary embolism in first trimester

902,891 women included
- IVF total: 3.5%
  - Fresh transfer: 25,382 women | Median age 33.6 years
  - Frozen-thawed transfer: 4946 women | Median age 34.1 years
  - Natural conception: 872,563 | 28 years
Fresh embryo transfer as associated with an increased incidence of
- VTE: Hazard ratio (HR) 8.96 (95% CI, 6.33 to 12.67)
- PE: HR 8.69 (95% CI, 3.83 to 19.71)
The incidence of thromboembolic events following frozen-thawed embryo transfer was not increased during the first trimester

Compared to natural conception, fresh embryo transfer had a more than eightfold increased incidence of VTE and PE in the first trimester
The authors suggest that frozen-thawed embryo transfer may be the preferred method of IVF embryo transfer to reduce maternal risk
In addition, the authors recommend that

…thromboprophylaxis could also be considered during early pregnancy after IVF with fresh embryo transfer

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