Results
We studied 9733 women, 1676 in the NC group and 8057 in the AC group. Baseline characteristics are presented in Table 1. Compared to women in the NC group, women in the AC group were younger, had higher BMI, a higher AFC, more no. of oocyte retrieved, and used more often an agonist protocol in the fresh cycle. They had thinner endometrium on the day of P administration and less often a triple-line pattern, more transferrable embryos and more good quality embryos transferred. Table 2 shows the pregnancy outcomes in NC and AC. Women in the AC group had a higher implantation rate, miscarriage and more male baby born compared with women in NC.
Univariate analysis was performed to evaluate the effect of each variable on the live birth rate (Table 3). Female age at oocyte retrieval and embryo transfer, BMI, infertility duration, secondary infertility, antagonist and other protocol in the fresh cycle, triple-line endometrial pattern (C) and single blastocyst transfer were negatively associated with live birth rate, while AFC, endometrial thickness on the day of P administration, no. of oocyte retrieved, no. of transferrable embryo, no. of good quality embryos transferred and blastocyst embryo transfer were positively associated with live birth rate.
A logistic regression model was then used to assess the association between endometrial preparation and clinical outcomes while adjusting for potential confounders presented in Table 4. In the adjusted model, type of endometrial preparation did not affect live birth (OR, 0.89; 95%CI, 0.79-1.01), clinical pregnancy (OR, 0.96; 95%CI, 0.85-1.09), preterm birth (OR, 1.09; 95%CI, 0.90-1.33) and ectopic pregnancy (OR, 0.77; 95%CI, 0.36-1.61), while AC significantly increased the miscarriage rate (OR, 1.38; 95%CI, 1.11-1.73, P=0.004).
Interaction and stratified analyses were shown in Table S1 and Table S2. Live birth rates were comparable in all subgroups. Higher miscarriage rate was observed in patients with AC in all subgroups of female age at oocyte retrieval, female age at embryo transfer, infertility duration, infertility type, AFC, endometrial thickness on the day of P administration, fertilization type, protocol in the fresh cycle, no. of oocyte retrieved, no. of transferrable embryo, no. of transferred embryos, no. of good quality embryos transferred, type of embryo transferred, triple-line endometrial pattern and single blastocyst transfer. There were no significant interactions in any of the subgroups (p >0.05 for all comparisons).