Multiple gestations in assisted reproductive technology: can they be avoided with blastocyst transfers?

Objective: Blastocysts are advanced-stage embryos with high implantation potential; theoretically, limited numbers of blastocysts can be used for embryo transfer to achieve good pregnancy rates with low multiple pregnancy rates. Clinical outcomes of a newly implemented blastocyst transfer program were evaluated.
Study Design: This study is a retrospective analysis of 553 blastocyst transfer cycles performed by a university-based in vitro fertilization program; risk factors associated with multiple gestations were analyzed.
Results: An average of 2.2 embryos were used for embryo transfer. The overall clinical pregnancy rate per embryo transfer was 45.1%; multiple gestation, twin, and triplet rates were 40.9%, 36.5%, and 4.3%, respectively. Multiple gestations increased significantly (1) when embryo transfer was done on day 5, (2) when > or =2 blastocysts were present on day 5, and (3) when maternal age was < or =30 years.
Conclusion: In spite of a conservative approach to the number of blastocysts used for embryo transfer, the overall multiple pregnancy rate was high, and triplet pregnancies did occur.