Objective: To determine the predictive value of 72-hour blastomere cell number on blastocyst development and to compare success rates of subsequent transfer based on the degree of blastocyst development.
Design: Retrospective clinical study.
Setting: Private assisted reproductive technology center.
Patient(s): Ninety-three women aged 32.0 +/- 5.1 years undergoing oocyte retrieval for IVF.
Intervention(s): Bipronucleate oocytes obtained from IVF were grown for up to 168 hours after fertilization and subsequently transferred at the blastocyst stage.
Main outcome measure(s): Percentages of embryos developing to blastocyst from 72-hour embryos by blastomere cell number and subsequent implantation and pregnancy rates of transferred blastocysts.
Result(s): Rates of blastocyst formation and expansion increased as cell numbers at 72 hours increased. Implantation rates were 43% for embryos transferred to women receiving only expanded blastocysts and 17% for embryos transferred to women receiving one or more less developed blastocysts. Pregnancy rates were higher for women receiving only expanded blastocysts than for women receiving one or more less developed blastocysts, although the difference was not significant.
Conclusion(s): More developed 72-hour embryos are more likely to become blastocysts and expand. Implantation rates are greater for the transfer of expanded rather than unexpanded blastocysts.