Predicting the probability of a live birth after a freeze-all based in vitro fertilization-embryo transfer (IVF-ET) treatment strategy

Abstract

Background: The predictors for live birth rate (LBR) following one episode of in vitro fertilization (IVF) cycle for patients using a "freeze-all" strategy are not entirely clear.

Methods: A retrospective cohort study utilizing a prediction model was developed to assess the relationship to the LBR. Women undergoing IVF with a freeze-all strategy were screened. Univariate models were first fitted for female age at oocytes retrieval/frozen-thawed embryo transfer (FET), body mass index (BMI), duration and etiology of infertility, previous IVF failures, total dose and duration of gonadotrophin, ovarian sensitivity index (OSI), number of oocytes collected, method of fertilization, number of embryos created, number and stage of embryos frozen, type and number of FET cycles, endometrial thickness (EMT)/pattern, hormone level on transplantation day, storage duration, number of embryos thawed and damaged thawed embryos, number and stage of embryos transferred and number of different quality embryos transferred. Variables with P<0.05 in the univariate model were selected for further analysis of the final multivariate discrete-time logistic regression model.

Results: A total of 7,602 women undergoing one ovarian stimulation resulted in 9,964 FETs, of whom 3,066 (40.33%) had a live-birth after their first FET and 3,929 (51.68%) after total FETs. The EMT and woman's age at oocyte retrieval were the most important predictors. In the first FET, the LBR of women with an EMT ≤8 mm [27.40%; 95% confidence interval (CI): (21.60-33.81%)] was significantly lower than that of women with EMT between 9 and 11 mm [36.51%; 95% CI: (34.25-38.81%)] and thicker than 12 mm [44.23%; 95% CI: (42.22-46.25%)] (P<0.05). The optimistic and conservative cumulative LBRs of women younger than 31 years [87.5%; 95% CI: (86.32-88.61%) and 63.04%; 95% CI: (61.36-64.69%)] were significantly decreased in women aged 31-35, 36-40 and >40 (P<0.001).

Conclusions: Our study provides an effective prediction model for a woman's chance of having a baby after a "freeze-all" policy. The use of EMT and female age as tools to identify LBR are shown to be justified, and repeated FETs cannot reverse the age-dependent decline in fertility.

Keywords: In vitro fertilization (IVF); freeze-all strategy; frozen-thawed embryo transfer (FET); live birth rates (LBRs); prediction model.

Figure 1

Trial flow chart. An overview of all started FET cycles and the overall reproductive outcomes. FET, frozen-thawed embryo transfer; Pos.hCG, positive human chorionic gonadotropin; CP, clinical pregnancy.

Figure 2

CLBRs stratified according to the categorical variables of positive significance in multivariate model. (A,B) Show the conservative and optimistic CLBRs stratified according to EMT, respectively. (C,D) Show the conservative and optimistic CLBRs stratified according to female age at oocyte retrieval, respectively. (E,F) Show the conservative and optimistic CLBRs stratified according to the number of oocytes collected, respectively. The conservative CLBRs were based on the assumption that none of the women who discontinued treatment would have had a live birth. These two curves show the best- and worst-case estimates of the CLBRs in the study group. The optimal CLBRs were based on the assumption that women who discontinued treatment would have had the same chance of a pregnancy resulting in a live birth as those who remained in treatment. These CLBRs reflect the worst- and best-case estimates, respectively. CLBRs, cumulative live birth rates; EMT, endometrial thickness.

Figure 3

Kaplan-Meier curves for CLBRs among all women in the study. The optimal CLBRs were based on the assumption that women who discontinued treatment would have had the same chance of a pregnancy resulting in a live birth as those who remained in treatment. The conservative CLBRs were based on the assumption that none of the women who discontinued treatment would have had a live birth. These two curves show the best- and worst-case estimates of the CLBRs in the study group. CLBRs, cumulative live birth rates.