A NOVEL APPROACH TO NATURAL FROZEN EMBRYO TRANSFERS (FET)

Natural FET studies to date determine the window of receptivity for implantation be calculated as either 6 days(d) after a natural LH surge (15IU/L) or 7d hCG trigger shot is administered induce ovulation in presence dominant follicle. All show no difference pregnancy outcome with approach. Our study sets out if our novel approach cycle (NC) FETs affects outcomes single autologous euploid embryo transfers. A retrospective chart review examined all transfers performed at academic medical center 2020. Day transfer based on progesterone values ≥ 1.5IU/L 2 consecutive days occurring 3d second elevated value. Primary outcome, were stratified into clinical intrauterine gestation (CIG), (NP), spontaneous abortion (SAB) and ectopic (ECT) secondary such endometrial thickness (ET) last visit prior FET, peak estrogen (E2) level, follicle size (P4) levels compared using chi-squared ANOVA analysis. In analysis, we calculation day published methodology (≥ 15IU/L) + 6d protocol would have been modified. Of 49 cycles, 33(67%) resulted CIG, 3(6%) SAB 1(2%) ectopic, 12(24%)NP. Within 4 groups, there differences ET, E2 size, first P4 suggestive ovulation. When comparing NC +6d, 25(51%) had change date. 13 patients their one later 12 prior. CIGs, 9 later. NPs, 3 prior.Tabled 1CIG (n=33)SAB (n=3)ECT (n=1)NP (n=12)P valueMean age (years)35.536.62935.90.49Avg ET (mm)11.412.313.09.20.21Avg Peak (IU/L)333.5359.7169.0368.70.55Avg (IU/L)5.03.92.86.10.25Avg Dominant Follicle Size (mm)21.119.518.021.00.63 Open table new tab data demonstrated that levels, not associated outcomes. There similar programmed during same time period (70.1% vs. 62.5%, p=.51). results suggest timing relation can vary may wider than was originally believed.