Controlled natural cycle IVF: experience in a world of stimulation.

A total of 134 controlled natural IVF (nIVF) cycles were reviewed retrospectively and compared with 370 stimulated IVF (sIVF) cycles. The clinical pregnancy rate per embryo transfer following nIVF was 27% and 47% in sIVF cycles for patients aged less than 35. However, natural cycle patients could attempt consecutive cycles with much less impact on their lives, both medically and financially. In patients under 35 years of age, the choice of controlled nIVF reduces the cost and risk to the patient, permitting her to have multiple, consecutive attempts, and cumulatively offers a clinical pregnancy rate which approaches that of sIVF. The multiple pregnancy rate in nIVF is significantly reduced compared with sIVF treatment cycles. In patients over 35 years of age the benefits of nIVF were much less evident (clinical pregnancy rate: 8% per embryo transfer) and the opportunity to transfer multiple embryos in these patients seems to be advantageous.