Objective: To compare the effects of oral micronized E(2) with transde
rmal E(2) on endometrial receptivity in women undergoing oocyte donati
on. Design: Prospective, randomized, crossover trial. Serum E(2) and P
concentrations were measured on cycle days 14 and 22 (luteal day +8).
Endometrial biopsies were obtained on day 22 and read in a blinded fa
shion for histology and beta-3-integrin expression. Setting: Universit
y-based donor oocyte program. Patients: Twenty-seven patients presenti
ng for donor oocytes. Main Outcome Measures: Endometrial histology and
P-S-integrin expression. Results: The endometrial glandular histology
in women given oral micronized E(2) was delayed by a mean of 1.6 days
in comparison to that of women given transdermal E(2) Seventy percent
of women given oral E(2) displayed a lag greater than or equal to 4 d
ays whereas 29.6% given transdermal E(2) displayed a similar lag. Seru
m E(2) levels were 1,194 +/- 108.8 pg/mL (mean +/- SEM; conversion fac
tor to SI unit, 3.671) in women on oral micronized E(2) and 117.4 +/-
14.0 pg/mL in those on transdermal E(2). Conclusion: The supraphysiolo
gic serum E(2) levels associated with oral micronized E(2) may have a
deleterious impact on endometrial receptivity. The development of more
physiologic hormone replacement protocols may enhance endometrial rec
eptivity and lead to improved clinical pregnancy rates.