Factors affecting the success of human blastocyst development and pregnancy following in vitro fertilization and embryo transfer.

OBJECTIVE: To determine the factors affecting blastocyst development and pregnancy after IVF and ET.

DESIGN: Retrospective analysis of data arising from a clinical trial.

SETTING: Private in vitro fertilization clinic.

PATIENT(S): Fifty-six patients aged < or = 40 years, undergoing IVF procedures for infertility, recruited specifically for blastocyst transfer.

INTERVENTION(S): All zygotes were cultured to days 5 or 6 after insemination, and one to four of the most advanced blastocysts were transferred to the patient's uterus.

MAIN OUTCOME MEASURE(S): Development of zygotes to blastocysts in vitro and pregnancy and implantation rates after ET.

RESULT(S): Fifty-one percent of all zygotes developed to blastocysts. Significant positive correlation between the number of blastocysts formed was observed with the number of oocytes, pronuclear zygotes, and eight-cell embryos formed. There was a negative correlation with male factor infertility. By day 5 or 6, 93% of the patients had at least one blastocysts, and the clinical pregnancy rate per transfer was 43% and the implantation per embryo transferred was 25%. No other clinical factor significantly affected the number of blastocysts formed, pregnancy rate, or implantation rate.

CONCLUSION(S): The numbers of oocytes, zygotes, and normally developing embryos in culture significantly affects the production of blastocysts in vitro. Male infertility significantly reduces blastocyst production. The number and the quality of the blastocysts transferred significantly influences clinical pregnancy rate.