In Frozen Embryo Transfer, Is High-Dose Aspirin Better?

Objective: This study aimed to evaluate whether high-dose aspirin during frozen embryo transfer (FET) improves pregnancy outcomes.

Methods: This is a retrospective study of 1207 FET cycles performed in 2022, excluding patients older than 40 years, with recurrent implantation failure, or with recurrent pregnancy loss. Pregnancy outcomes, miscarriage rates, number of clinic visits, and obstetrical outcomes were compared between 2 groups: a group with 81 mg aspirin (January-June 2022) and the other group with 162 mg aspirin (June-December 2022). Aspirin was started on day 1 of the cycle and continued until delivery. Patients were divided into 2 endometrial preparation groups. The modified natural cycle group received ultrasound monitoring, trigger shot at 15 mm follicle size and 7 mm endometrial thickness. The artificial cycle group received estrogen supplementation until endometrial thickness reached ≥7 mm, followed by progesterone.

Results: Pregnancy outcomes were similar in both endometrial preparation protocols. The subgroup analysis revealed a trend of lower clinical pregnancy rates and lower live birth rates in the 162 mg aspirin group for both preparation protocols. The only significant complication was hematoma formation, which was higher in the 162 mg group. Multiple regression analysis showed that a higher aspirin dosage and endometrial preparation method significantly increased miscarriage rates.

Conclusion: High-dose aspirin during FET cycles may negatively impact pregnancy outcomes, increasing miscarriage risk. Lower-dose aspirin (81 mg) may be more beneficial.