[FIVNAT evaluation of frozen embryo transfers from 1987 to 1994].

Between January 1987 and December 1995, 15676 thawed embryo transfers were included in the Fivnat register. During this period, the per transfer pregnancy rate increased from 11.5% to 16.0%. Medical practice, results and pregnancy factors were analysed on 11584 transfers collected until december, 1994. The relationship between patients' characteristics or OPU cycles variables and pregnancy was analysed on a sub sample of 8483 cycles of frozen embryo transfers for which the files could be related to the original cycle which gave rise to the frozen embryos. The per transfer pregnancy rate is decreased when the transfer cycle combines hormonal substitution and GnRH analogue, or includes Clomiphene Citrate in the stimulation regimen. It increases with the number of transferred embryos (from 7.3% with 1 embryo to 16.5% with 3, and decreases when the women's age increases (3.2% after 41 years). It is higher when GnRH analogues were not used in the OPU cycle, and higher with FSH when the long protocol is used. The pregnancy rate is also higher when the OPU cycle resulted in a clinical pregnancy. Abortion and ectopic pregnancy rates are close to those resulting from transfers of fresh embryos. The multiple pregnancy rate is lower as are the preterm birth rate and hypotrophy. The malformation rate at birth is close to that of fresh embryo transfers after IVF.