OBJECTIVE: To assess the association between number of embryos transferred and a measure of assisted reproductive technology success that emphasizes good perinatal outcome.
METHODS: We analyzed assisted reproductive technology cycles initiated in 2011 that progressed to fresh embryo transfer among women using autologous oocytes and reported to the U.S. National Assisted Reproductive Technology Surveillance System (n=82,508). Percentages of good perinatal outcome (live birth of a term [at or after 37 weeks of gestation], normal birth weight [2,500 g or greater] singleton) were stratified by prognosis (favorable, average, less favorable), age, embryo stage (day 3, day 5), and number of embryos transferred. Differences in the percentages by number of embryos transferred were evaluated using Fisher’s exact test with Bonferroni correction.
RESULTS: Among patients younger than 35 years with a favorable prognosis, chances of a good perinatal outcome were higher with transferring a single (compared with double) day 5 (43% compared with 27%) or day 3 embryo (36% compared with 30%). Likewise, a higher chance of a good perinatal outcome was observed with transferring a single day 5 embryo in patients 35–37 years old with a favorable prognosis (39% compared with 28%) or patients younger than 35 years old with an average prognosis (35% compared with 26%). A higher chance of good perinatal outcome was associated with transferring two (compared with one) day 3 embryos among patients aged 40 years or younger with an average prognosis or patients younger than 35 years old with a less favorable prognosis.
CONCLUSION: The association between number of embryos transferred and the birth of a term, normal birth weight singleton is described. Among patients younger than 35 years of age undergoing in vitro fertilization with a favorable prognosis, the highest chance of good perinatal outcome is associated with a single embryo transfer.
LEVEL OF EVIDENCE: II