Couples with a high likelihood of having twins when transferring two embryos should seriously consider transferring a single blastocyst. These couples include women age 37 or younger, couples using donor eggs or any other patient that may be at increased risk to have a miscarriage or medical complications when becoming pregnant with twins (e.g., certain uterine abnormalities, previous twin miscarriages). Importantly, the decision to transfer a single blastocyst should be made on the day of transfer, provided that there is at least one additional blastocyst for cryopreservation.