Nov. 11, 1999 (New York) -- Since in vitro fertilization (IVF) was first performed in 1978, births of triplets, quadruplets, and more have become a common and sometimes dangerous complication of infertility treatments. Now researchers reporting in the Nov. 17 issue of TheJournal of the American Medical Association say the risks of multiple births can be minimized by reducing the number of fertilized eggs transferred to a woman's uterus.
In IVF, eggs are removed from the ovaries, mixed with sperm in the laboratory, and transferred back to the uterus where attachment, or implantation, of the embryo occurs. Since not every fertilized egg will implant and result in pregnancy, physicians often transfer more than one fertilized egg, which can result in multiple births. Multiples are at increased risk for complications such as preterm delivery, low birth weight, birth defects, fetal and infant death, and long-term illness and disability. Twins have a fivefold increased risk of death in the first year of life, while triplets or more have a 13-fold increased risk as compared to single births.
"The decision about how many embryos to transfer is complicated, and our study confirms that," the study's lead author, Laura A. Schieve, PhD, tells WebMD. Schieve is with the division of reproductive health, National Center for Chronic Disease Prevention and Health Promotion at the CDC in Atlanta.
Schieve's study, based on over 35,000 IVF procedures in the U.S., found that multiple birth rates varied by age and number of embryos transferred. Multiple birth rates were 23% for women ages 20 to 29 with two transferred embryos. That rate gradually went down with age. Women ages 40 to 44 had an 11% rate of multiple births with two transferred embryos. Those rates increased when three embryos were transferred in the youngest age group to 46% but were less than 25% in women in the oldest age group, even if five embryos were transferred.
"The bottom line is that we would recommend couples and providers discuss both the benefits and risks of how many embryos to transfer when they are making decisions about IVF," Schieve says.
Until recently, the American Society for Reproductive Medicine (ASRM) and its affiliate, the Society for Assisted Reproductive Technology (SART), recommended that no more than three embryos should be transferred in women under age 35. However, on November 11, the ASRM announced that it is changing those recommendations, which are used as guidelines for physicians who perform IVF.
The new guidelines state that the number of embryos to transfer should be no more than two in women under age 35 with especially good prognosis of giving birth, no more than three in women under age 35 with good prognosis, no more than four in women age 35 to 40 with above average prognosis and no more than five in women age 40 or older with below average prognosis or a history of previous failed IVF cycles. Schieve's study found that more than one-third of women over age 40 had five or more embryo transfers.
"We want to maximize the chances of a successful pregnancy and decrease the risk of multiple [pregnancy]," says Phil McNamee, MD, president of SART, in a statement to the media. "This change is the result of careful monitoring of the outcomes of assisted reproductive technology procedures. Our 10-year effort to collect data from all our member clinics, joined these last two years by the CDC, enables us to give our members, and the public, the best advice on how to optimize infertility treatments while reducing risks."