Replacement of frozen-thawed embryos in artificial and natural cycles: a prospective semi-randomized study

This prospective partly-randomized study assessed the relative efficacy of two strategies of patient management for the replacement of frozen-thawed embryos. A luteinizing hormone-releasing hormone (LHRH) agonist was used to induce a temporary hypogonadism in a group of patients who were then prepared for implantation by endometrial priming with hormone replacement therapy (HRT): oral oestradiol valerate and then oestradiol valerate and injections of progesterone. A second group of patients had their frozen-thawed embryos replaced during their natural cycles. Of the 84 patients treated with the LHRH regimen, 80 had embryos replaced and 16 (20%) clinical pregnancies were established. Of the 78 patients treated with natural cycles, 70 had embryos replaced and 14 (20%) achieved clinical pregnancies. There were no statistical differences between the two groups in terms of age, obstetric history, duration of infertility, number of oocytes retrieved and fertilized or the number of embryos frozen following ovarian stimulation in the embryo 'generating' cycle. In terms of pregnancy rates, both protocols were equally effective. However, the LHRH-HRT protocol was of great value in the management of oligomenorrhoeic patients and in establishing standard conditions for implantation in cyclic patients.