Relationships between embryo transfer results and ovarian response and in vitro fertilization rate: analysis of 186 human pregnancies.

We studied the relationships between "pretransfer" parameters (number of follicles, oocytes, and embryos) and the result (occurrence and quality of pregnancy) obtained by transferring one, two, or three embryos. The analysis concerns 186 pregnancies compared with 186 implantation failures. The chances for an oocyte to cleave or for a pregnancy to continue decreased when the number of preovulatory follicles increased. The number of transferred embryos increased with oocyte cleavage rate in nonpregnant patients and in patients with an ongoing pregnancy, but such a relation was not found in the case of failed pregnancy (biochemical pregnancies and abortions). Failed pregnancies occurred in patients who demonstrated the highest oocyte cleavage rate (94.1%), compared with 81.2% for implantation failure and 84.8% for ongoing pregnancy (P less than 0.01). The cleavage rate was also higher in cases of multiple, compared with single, ongoing pregnancies after the transfer of three embryos (79.7% versus 64.5%, P less than 0.001). An important finding was the higher survival rate after triple-embryo transfer in patients, yielding numerous oocytes. The survival rate (fetuses per transferred embryos) after the transfer of three embryos was 14.9% in patients yielding five oocytes, versus 7.7% in patients yielding 3.4 oocytes (P less than 0.05). These results are related to oocyte and embryo viability and uterine ability for pregnancy.