To our knowledge, this is the first study to report estimates of live birth rates and ClBRs across complete cycles among large sample population with freeze-all strategy during ten years. Although many studies about IVF have been reported, most of them were limited by small samples, conventional IVF strategy, and the use of pregnancy or live birth rate per cycle as the primary outcome [15, 16]. Few researches reported the cumulative live birth rate per patient among population using freeze-all strategy. This study conducting in 20687 patients reported the conservative and optimal estimates of CLBRs, which could reflect the chance of success for patients undergoing IVF treatment with freeze-all strategy. In this study, we presented the clinical outcome of IVF in a patient-anchored approach and all cycles were attached to the patient receiving IVF treatment. Despite the live birth rate declined with the increasing number of cycles, the CLBRs increased up to and including the fifth cycle in the whole cohort. The conservative and optimal estimates of CLBRs in our population of more than 20000 patients undergoing up to five complete cycles of IVF treatment were 64.11% and 80.41%, respectively. As the CLBRs may be underestimated or overestimated by the conservative or optimal estimated, the ‘realistic’ CLBR for our population was probably between the two estimates.
CLBRs after IVF have been reported across nations. The CLBRs for the conservative and optimal estimates (51% and 72%) after six complete cycles reported by Malizia et al. from a large center in Boston were lower than these in our study (64.34% and 83.40%). Comparing with the conservative and optimal estimates of CLBRs after six complete cycles in the UK (43.90% and 75.50%) and Belgium (54.10% and 76.30), corresponding figures from our research were slightly higher[5, 17]. We speculate that the higher CLBRs in our study is related with our treatment protocol—freeze all strategy, which has been reported that could increase pregnancy rate and live birth rate by avoiding the potential deleterious effects of controlled ovarian stimulation on the endometrium. In addition, the differences in age structure, causes of infertility between our study population and previous study population may also contribute to the different CLBRs across nations. So randomized controlled trials are needed to verify the finding in future study.
As we all known, maternal age was an important factor affecting the fertility in the natural population. In our study, the CLBRs also declined with the increasing of the age. Leridon reported the final proportions of women ending in a live birth was 94% for women starting attempts to conceive at age 30 years, 86% for those starting age 35 years and 65% for those starting at age 40 years in the natural population.Our optimal CLBRs after seven complete cycles for women younger than 31 years, aged 31 to 34 years, aged 35 to 37 years, and aged between 38 and 40 years were 95.81%, 90.80%, 81.54%, and 58.25%, respectively. These figures proved that IVF could reduce the gap in the probability of having a live birth for the infertility women no more than 40 years. However, the possibility of delivering a live baby was only 19.45% for women older than 40 years after seven complete courses of IVF treatment. This suggested that IVF could not completely compensate for the decrease of fertility among women older than 40 years. In addition, our age-stratified CLBRS also could provide individualized information about the chance of success for patients of any age.
In this study, we constructed two models to estimate the chances of a live birth over one or more complete cycles. For patients embarking on IVF following freeze-all strategy, model one could predict the probability of having a baby over multiple complete cycles using the patient’s baseline characteristics, including age, infertility type and causes of infertility. But for patients finishing the first complete cycle, the treatment information at complete cycle one was available. So we developed model two by adding the treatment information to make the prediction more precise. In model one, age was an important predictor for the chance of live birth. In model two, besides age, the number of oocyte retrieved at complete cycle one also played an important predictive role. The two models can be used by patients before starting IVF and patients after the first complete cycle to estimate their probability of having a baby for making treatment decisions.
Many studies have been conducted to predict the success of IVF. David predicted the cumulative chances of having a baby over a complete package of IVF, but this model only applied to population using the conventional IVF strategy . R.K. Dhillon also made a prediction models for live birth following IVF, but this study included patients undergoing their first fresh cycle of IVF and was limited to use prior to first cycle only . Our study is the first to estimate the probability of having a baby over multiple complete cycles of IVF for patients following strategy, which can be used as a guiding tool in making decisions about treatment with freeze-all protocol.
Our research has some limitations. First, we did not adjust factors such as body-mass-index, smoking and alcohol use in our model, as these variables were unavailable in our IVF database . Second, this model is developed for freeze-all strategy, so patients undergoing IVF treatment with conventional IVF strategy could not estimate their chance of having a live birth using this model.