Purpose: To examine the effect of low and very low estradiol responses in oocyte donors receiving gonadotropins on clinical outcomes of donor in vitro fertilization (IVF) cycles and to identify possible mechanisms responsible for low estradiol response.
Methods: This is a retrospective cohort study of oocyte donors undergoing antagonist IVF cycles with progression to oocyte retrieval between January 2010 and December 2016 at a single urban academic fertility center. Oocyte yield, fertilization rate, blastocyst rate, percentage of normal embryos on preimplantation genetic screening (PGS), pregnancy outcomes, and follicular fluid steroid profiles were compared between donors with normal estradiol response and those with low estradiol response.
Results: Three hundred sixty-six antagonist oocyte donor IVF cycles were identified: 42 cycles had a normal estradiol response (NE2), defined as peak serum estradiol (E2) of over 200 pg/mL per retrieved oocyte; 140 cycles had an intermediate estradiol response (iE2), defined as peak serum E2 between 100 and 200 pg/mL per retrieved oocyte; 110 cycles had a low estradiol response (LE2), defined as peak serum E2 between 50 and 100 pg/mL per retrieved oocyte; and 74 cycles had a very low estradiol response (vLE2), defined as peak serum E2 less than 50 pg/mL per retrieved oocyte. LE2 cycles resulted in a greater number of mature oocytes (22.4 vs. 13.6, p < 0.017), and fertilizations versus NE2 donors (18.5 vs. 10.7, p < 0.017), although the number of transferred or cryopreserved blastocysts were similar between groups (8.6, 6.9 vs. 4.8, p = 0.095, p = 1). The percentage of chromosomally normal embryos after PGS was similar between LE2, vLE2, and NE2 cycles (66.4, 71.8 vs. 63.1%, p = 0.99, p = 1). Pregnancy outcomes were similar between LE2, vLE2, and NE2 cycles. Serum AMH obtained on the day of peak E2 was similar to baseline serum AMH and did not differ between LE2 versus NE2 cycles. Follicular fluid E2 levels paralleled serum E2 levels and were lower in LE2 cycles versus NE2 cycles.
Conclusion: The prevalence of very low E2 responses in donors appears to be high (20.2%). In contrast to autologous IVF cycles, LE2 does not portend poor outcomes in oocyte donors.
Keywords: COS response; Estradiol; Follicular fluid; In vitro fertilization; Oocyte donor.