April 14, 2004 -- More than ever, infertile women in the U.S. are undergoing assisted reproduction techniques and are successfully having babies. And according to a new study, there is more good news: Multiple-infant pregnancies involving three or more fetuses are declining.
While roughly one in three pregnancies achieved through in vitro fertilization or other assisted reproduction techniques still involve multiple fetuses, pregnancies with triplets or more dropped from about 11% in 1997 to 7% in 2001.
Multiple-infant pregnancies are associated with complications for both the mother and her baby, including much higher rates of miscarriage, premature birth, higher need for cesarean delivery, birth defects, and higher rates of infant death. Assisted reproduction techniques (ART) are responsible for a 100-fold increase in the occurrence of multiple-infant births over the past two decades.
"It is very good news that pregnancy rates continue to go up and that high-order birth rates continue to go down," the study's lead researcher, Tarun Jain, MD, tells WebMD. But the number of twin births did not change significantly, and he says the next big challenge in the treatment of infertility will be to decrease the rates of twin pregnancies because of assisted reproductive techniques.
Twin births accounted for just under 30% of pregnancies resulting from assisted reproduction in 2001 -- slightly higher than the rate for 1997.
Live Births Per Cycle
Jain and colleagues from Boston's Brigham and Women's Hospital analyzed data on assisted reproductive techniques reported to the CDC from 1995 until 2001 by fertility clinics in the U.S. They also reviewed figures on the rates of twin, triplet, and higher-order pregnancies and births to examine trends in the U.S. from 1980-2001.
Their findings are published in the April 15 issue of TheNew England Journal of Medicine:
- The percentage of pregnancies achieved at each attempt at assisted reproduction increased from 24% in 1995 to 33% in 2001.
- The percentage of live births occurring per assisted reproduction attempt increased steadily from an average of 19% in 1995 to roughly 27% in 2001.
Assisted reproduction techniques involve union of the egg and sperm in the lab, then placing a number of fertilized eggs back into the women. The increase in pregnancy rates and live births occurred even though the average number of embryos transferred per ART attempt declined from roughly four in 1995 to three in 2001.
Jain and study co-author Mark D. Hornstein, MD, say the findings validate the notion that decreasing the number of transferred embryos results in a reduction in multiple-infant pregnancies without affecting overall pregnancy rates.
In an effort to reduce high-order pregnancies, several European countries have passed laws restricting the number of embryos that can be transferred each time assisted reproduction techniques are attempted. There are no such restrictions in the U.S., but the nation's top infertility group now has guidelines that call for a maximum of two embryos transferred per attempt at assisted reproduction for infertile women with the most favorable prognoses for becoming pregnant -- usually women under 35 years old.
In women with a below average chance of becoming pregnant with assisted reproduction techniques, a maximum of five embryos are transferred. These are women who are 45 and older and who have had numerous failed attempts at assisted reproduction.
Twin Births Troubling
American Society for Reproductive Medicine Executive Director Robert W. Rebar, MD, tells WebMD that the group is considering tightening the guidelines even further to address the issue of twin births.
"The fact that we have not lowered the percentage of twin births is of concern," he says. "Most people don't appreciate the fact that, like higher-order births, twin births are associated with greater obstetrical and neonatal morbidity and mortality."
He says single-embryo transfer will become a more attractive option for many infertile couples as assisted reproduction laboratories get better at freezing embryos.
"It is almost as cheap to freeze embryos and implant them one per cycle as it is to implant multiple embryos during a single cycle," he says. "This is an evolving practice, but I do believe that it is the direction that we are going in and that it will lead to a reduction of multiple births."