Frozen embryo cycles
Of all allocated patients, the total number of initiated FET cycles with thawed embryos was 665 in the PPOS group and 259 in the long agonist group. In the PPOS group, 662/665 (99.5%) had one frozen embryo transfer compared to 257/259 (99.2%) in the long agonist group. In the majority of FET cycles Day-3 embryos were thawed and transferred. Presence of top quality of embryos after thawing and endometrial thickness were similar between the two groups. More women had double embryo transfer in the frozen embryo cycles in the agonist group (75.5%) than in the PPOS group (50.8%). Hormonal cycles used for endometrium preparation were used in more FET cycles in the PPOS group 482/662 (72.8%) compared to 104/257 (40.5%) in the long agonist group (P < 0.001) (Table III).
Women in the PPOS group were less likely to have a live birth following their first FET cycle 139/433 (32.1%) compared to those in the long agonist group 85/192 (44.3%) (OR: 1.721; 95% CI: 0.588–0.884; P = 0.003). However, this difference disappeared after inclusion of additional FET cycles. Of all FET cycles, a total of 206/662 (31.1%) cycles resulted in a live birth in the PPOS group versus 110/257 (42.8%) in the long agonist group (OR: 0.727; 95% CI: 0.607–0.871; P <0.001) .The implantation rate of total FET cycles was also lower in the PPOS group compared with that in the agonist group 293/1004 (29.2%) and 157/455 (34.5%) (OR: 0.846; 95% CI: 0.721–0.992; P = 0.041) (Table IV).
In regression analyses with embryo transfer day and endometrium preparation as the independent variables, we found no impact on the total LBRs from FET for embryo transfer day (OR = 0.87; 95% CI 0.35–1.67; P = 0.51). But for endometrium preparation, we found a significant effect (OR = 0.59; 95% CI: 0.25–0.96; P = 0.03) (data not shown in table). Hormonal FET cycles were correlated with lower total FET LBRs.