Objective:  To evaluate the effect of low-dose aspirin use in oocyte (egg) donation recipients with an endometrial thickness of less than 8 mm.

Design:  A prospective, randomized study.

Setting:  An oocyte donation program in a private infertility practice.

Patients:  Twenty-eight recipients undergoing oocyte donation who failed to develop an endometrial thickness of at least 8 mm in a previous evaluation cycle.

Intervention:  Fifteen recipients received low dose aspirin (81mg/d) in addition to standard hormone replacement for an oocyte donation cycle. The remaining 13 recipients did not receive aspirin.

Main Outcome Measures:  Clinical pregnancy rates, delivery rates, implantation rates, and change in endometrial thickness were compared in the aspirin and nonaspirin groups.

Results:  There was no demonstrable increase in endometrial thickness in the aspirin treated group. However, there was a statistically significant increase in implantation rates in the aspirin-treated group (24 percent versus 9 percent) and in implantation rates and clinical pregnancy rates in the aspirin-treated group when the final endometrial thickness was less than 8mm.

Conclusion:  Low-dose aspirin therapy improves implantation rates in oocyte donation recipients with a thin endometrium.