Inter-Cycle Variation in Endometrial Thickness in Fresh Embryo Transfer Cycles: Predictors and Association with Pregnancy Outcome

Abstract

Background: The use of intracytoplasmic sperm injection (ICSI) has increased substantially worldwide, primarily in couples with non-male factor infertility. We recently published the results of a large randomised controlled trial (RCT) comparing ICSI and IVF showing no significant improvement of ICSI over IVF in couples with normal semen concentration and motility. Here, we assess the cost-effectiveness of ICSI in these couples, with additional attention for subgroups. Aim: To evaluate the inter-cycle variation in endometrial combined thickness (ECT) in fresh embryo transfer cycles Method: This was a retrospective cohort study in a single university affiliated fertility clinic in Chengu, China. We studied women undergoing IVF/ ICSI treatment in a fresh stimulated cycle, and measured endometrial combined thickness on the day of HCG trigger in consecutive stimulated IVF/ICSI cycles. Inter-cycle variation in ECT was the main outcome measure. Secondary outcomes were the relationship between ECT and treatment outcomes clinical pregnancy, live birth and miscarriage. Results: The mean ECT in consecutive fresh stimulated cycles was 10.28 ⊠ 2.15mm in cycle 1 (n=7038), 9.93 ⊠ 2.11mm in cycle 2 (n=1287), 9.49 ⊠ 2.22mm in cycle 3 (n=148) and 8.63 ⊠ 1.82mm in cycle 4 (n=17) (p [Formula: see text]0.01.). An incremental increase in the clinical pregnancy rate was demonstrated for each additional millimetre in ECT up to a threshold level of 12-15mm. There was no evidence of systematic bias on the visual assessment of the Bland Altman plot in women undergoing 2 consecutive cycles of treatment (mean bias 0.46, (95% limits of agreement -5.62 to 5.65)). Multivariate predictors of ECT were the number of previous treatment cycles, secondary infertility, infertility diagnoses of anovulation, endometriosis, male factor or unexplained infertility and the number of follicles greater than 14mm on the day of HCG trigger. There was a small, significant interaction between female age and ECT on the outcome clinical pregnancy. Conclusion: There is a slight decrease in mean ECT in women undergoing consecutive stimulated IVF/ICSI cycles which is potentially explained by the increased occurrence of pregnancy with thicker ECT. Each millimetre increase in late follicular ECT increases the odds ratio of clinical pregnancy to a threshold level of 12-15mm.