Elective Single-Embryo Transfer versus Double-Embryo Transfer in In Vitro Fertilization

Both premature birth and perinatal death are likelier after in vitro fertilization (IVF), chiefly because of a high incidence of multiple births. This in turn is associated with the number of embryos transferred. This study tested the hypothesis that, in women less than 36 years of age, pregnancies yielding at least 1 live birth after transfer of a single fresh embryo (and, if no live birth results, the subsequent transfer of a frozen–thawed embryo) would equal those in patients who simultaneously received 2 fresh embryos. Another prediction was that single-embryo transfers would lower the rate of multiple gestations. Participants were having their first or second IVF cycle and had 2 or more good-quality embryos available. A total of 330 women were randomly assigned to receive a single embryo, whereas 331 received 2 embryos. The rate of pregnancies resulting in at least 1 live birth was 39% after single-embryo transfer and 43% after double-embryo transfer. Although not demonstrating equivalence of the 2 methods, these figures do indicate that the rate of live births after elective single-embryo transfer ranged from 12% below to 3% above that for double-embryo transfers. When a single fresh embryo was transferred, live births were significantly less frequent than with double-embryo transfer (28% vs. 43%). After subsequent transfer of a frozen–thawed embryo, the live birth rate was 16%. Rates of multiple births were 33% after double-embryo transfer and less than 1% after single-embryo transfer. In women younger than 36 years in this large study, transferring a single fresh embryo, and later a frozen–thawed embryo if necessary, markedly lowered the incidence of multiple births. The rate of live births was lower than after double-embryo transfer, but the difference was not substantial. These findings strongly endorse elective single-embryo transfer for women in this age range.