Only women's age and the duration of infertility are the prognostic factors for the success rate of natural cycle IVF.

Purpose: It is controversial who should be recommended to undergo natural cycle IVF (NC-IVF). Therefore, objective prognostic criteria which are already known at the time of counselling were defined.

Methods: A retrospective observational study was performed with 201 couples (age 34.7 ± 4.1) undergoing 311 NC-IVF treatments with 201 transfers, corresponding to a transfer rate of 65.3%. The first cycle resulting in a transfer of one embryo was further analysed. Clinical pregnancy and live birth rates were analysed.

Results: Pregnancy rate and live birth rates per first cycle were 21.9% and 13.2%, respectively. Groupwise comparison revealed the following clinical pregnancy/live birth rates per transfer cycle: duration of infertility 1-2 years 34.3/25.7%, 3-4 years 21.8/14.9% and > 4 years 9.1/4.5%. Women's age  < 34 years 26.3/22.4%, 34-37 years 25.7/18.9% and 38-42 years 15.7/3.9%. Linear regression analysis showed that pregnancy and live birth rate correlated negatively with the duration of infertility and that live birth rate but not pregnancy rate correlated negatively with increasing female age. In contrast, AMH and infertility factors did not correlate with the success rate. Statistically significant correlations remained if a multivariate logistic regression analysis was performed, supporting further that the duration of infertility (OR 0.61, 95% CI 0.42-0.86) (P = 0.006) and female age (OR 0.87, 95% CI 0.78-0.95) (P = 0.008) are the predictors for live birth rates in NC-IVF transfer cycles.

Conclusions: Based on the success rates, NC-IVF can especially be recommended for women with short duration of infertility and young age, whereas older women and those with long duration of infertility are not the best candidates for this technique.