TRANSFER OF CRYOPRESERVED-THAWED PREEMBRYOS IN A NATURAL CYCLE OR A PROGRAMMED CYCLE WITH EXOGENOUS HORMONAL REPLACEMENT YIELDS SIMILAR PREGNANCY RESULTS

Objective: To examine the results of 7 years of thawed ET during natur al or controlled cycles using exogenous steroids. Design: Retrospectiv e evaluation to compare implantation and pregnancy rates with two prot ocols for transfer of cryopreserved-thawed pre-embryos. Setting: Terti ary care academic center. Patients: From January 1987 to December 1993 , 521 patients who were <40 years of age underwent 628 thawed embryo t ransfers. Main Outcome Measure: Pregnancy and implantation rates per t hawed embryo transfer cycle. Results: A total 1,987 pre-embryos surviv ed the thawing process and were used in 628 thaw-transfer cycles. Tran sfer was performed in a natural cycle 2 days after the LH peak or on d ay 17 of a programmed cycle using a GnRH-agonist and hormone replaceme nt therapy protocol; 182 pregnancies were established (182/628; 29%). Similar pregnancy rates were seen in the natural cycle (112/398; 28%) and the programmed cycle (70/230; 30%). The implantation rates were si milar in the two methods of transfer cycles (11.9% versus 10.3%, natur al versus programmed cycle). There were no significant differences in clinical or ongoing pregnancy rates in a natural or programmed cycle, correcting for the number of cryopreserved-thawed pre-embryos transfer red. Patient's age at the time of freezing and the number of cryoprese rved-thawed pre-embryos transferred are more important determinants of pregnancy than the type of cycle in which transfer occurs. Conclusion : Transferring cryopreserved-thawed pre-embryos in a natural or progra mmed cycle yields similar pregnancy results.