P-593 Low dose clomiphene citrate does not reduce implantation rates - a cohort study based on modified Natural Cycle IVF

Abstract

Abstract Study question Does low dose clomiphene citrate (CC) reduce implantation and eventually pregnancy and live birth rates? Summary answer Low dose CC does not reduce implantation rate and pregnancy and live birth rates – based on the model of modified Natural Cycle IVF (NC-IVF). What is known already CC is commonly used for ovulation induction in the treatment of anovulation or idiopathic infertility. It is also added to NC-IVF cycles to mildly stimulate follicular growth and to inhibit LH surge. CC reduces endometrial thickness and affects endometrial function. Therefore it is assumed that CC negatively affects implantation and thereby reduced pregnancy and live birth per embryo. However, previous studies have shown inconsistent results as previous studies mainly calculated pregnancy rates per cycle but not implantation rate per embryo. Study design, size, duration This cohort study included embryos transferred in NC–IVF and CC-NC-IVF cycles. Women with a maximum age of 42 years were treated at a university hospital between 2011 and 2016. Clinical pregnancy rate and live birth rate per embryo transferred and miscarriage rate per amniotic sac were calculated. Participants/materials, setting, methods A daily dose of 25mg of CC starting on day 5-7 of the cycle until the day of ovulation trigger was applied. A modified mixed effect Poisson regression model was used to account for the number of cycles in the same women and the number of embryos in the same cycle to achieve rate ratios (RR). Adjustment for maternal age, parity, type of infertility, duration of subfertility and indication for IVF were made. Main results and the role of chance 499 couples underwent a total of 1043 IVF cycles, 453 NC-IVF and 590 CC-NC-IVF cycles. Baseline characteristics of both groups were not different. The additional administration of CC did neither decrease clinical pregnancy rate (aRR 1.16; 95% CI: 0.90 – 1.50)[MV1] nor live birth rate per transferred embryo (aRR 1.20; 95% CI: 0.89 – 1.62). Miscarriage rate was also not different in CC-NC-IVF compared to NC-IVF (aRR 1.05; 95%: CI 0.63 – 1.76). Limitations, reasons for caution This study does not allow to draw any conclusions regarding the effect of higher CC dosages. As randomization was not performed, some bias regarding the choice of IVF treatment cannot be completely excluded. Wider implications of the findings As this study revealed for the first time that low dose CC does not affect implantation, low does CC can be used for many different treatments. However, further studies are required to evaluate if this also applies to higher CC dosages. Trial registration number not applicable