A theoretical model for single blastocyst transfer

Objective  To elucidate the relationship between embryo grade and ART outcomes and determine how to decrease multiple pregnancy rates by assigning patients to single embryo transfer (SET) instead of dual embryo transfer (DET) according to embryo grade and/or availability. Design  Retrospective medical record review. Setting  IVF fertility center. Patients  247 women undergoing day 5 DET after in vitro fertilization or intracytoplasmic sperm injection treatment. Methods  We retrospectively investigated embryo grade and outcomes on day 5 DET and calculated theoretical multiple pregnancy rates by assigning patients to SET instead of DET according to a combination of embryo grades and availability. Main Outcomes Measures  Implantation, pregnancy, multiple pregnancy, expected pregnancy and expected multiple pregnancy rates. Results  Embryo grade affects implantation rates so that embryo transfer of at least one embryo with grade ≥ 3BB resulted in high multiple pregnancy rates as well as high pregnancy rates. By performing DET, the clinical pregnancy rate was 39.9% with a multiple pregnancy rate of 33.3%; however, had SET been performed with an embryo graded 3BB or better, theoretical calculated pregnancy rates would have dropped to 35.8% but with a multiple pregnancy rate of 7.2%. Conclusions  Our model showed that cases having at least one embryo with grade ≥ 3BB might serve as suitable candidates for SET.