SAN FRANCISCO — The transfer of more than one embryo during in vitro fertilization has a substantial adverse residual effect on intrauterine growth—even when only one fetal heart is detected on early ultrasound, findings from a large historical cohort study suggest.
A review of data from 23,999 singleton live births resulting from assisted reproductive technology cycles performed from 2004 to 2006 showed that the risk for intrauterine growth restriction increased significantly with the number of embryos transferred; compared with one embryo transferred, the risks were increased by 16%, 24%, 34% and 56% when two, three, four, or five embryos were transferred, respectively, Barbara Luke, Sc.D., reported at the annual meeting of the American Society for Reproductive Medicine.
No differences were seen in preterm birth weights based on the number of embryos transferred.
Also, factors such as maternal age, birth weight (mean of 3,243 g), length of gestation (mean of 265 days), and birth weight for gestation (z score, mean of 0.30 standard deviation units) did not differ significantly across the embryo transfer groups, noted Dr. Luke of Michigan State University, East Lansing.
Preterm birth was defined as birth prior to 37 weeks' gestation, and intrauterine growth restriction was defined as a z score of less than −1. The z score is a measure of intrauterine growth adequacy, with a mean of 0 (indicating the 50th percentile of intrauterine growth), she explained.
The findings support the theory that there is a critical period during which abnormal placentation related to the transfer of multiple embryos may adversely affect pregnancy—even for singletons, Dr. Luke concluded.
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