BioEd Online

Doctors should slash the health risks for mothers and children associated with in vitro fertilization (IVF) by transferring only one embryo into the uterus after treatment, thereby cutting the rate of multiple births, researchers urged this week.

The high rate of twins, triplets or higher multiple births is one of the most pressing problems in fertility treatment. Multiple births are associated with health problems for the mother such as high blood pressure, and increase the risk that their babies will be born prematurely or with low birth weight.

The high rate occurs because doctors routinely place several embryos into the womb during treatment. This practice continues because both doctors and patients widely believe that it boosts the chances of pregnancy.

Not so, said experts at the American Society for Reproductive Medicine (ASRM) meeting in Philadelphia on 21 October. They presented several studies showing that, using modern techniques for growing and selecting healthy embryos, the pregnancy rate after transferring one embryo is just as high as that after transferring two.

Twin pregnancies reduced

Pia Saldeen and her colleagues at IVF Klinken CURA in Malmö, Sweden, examined the pregnancy rate in Swedish fertility clinics. In January 2003, health authorities in the country banned the transfer or more than one embryo at a time except in exceptional circumstances.

Saldeen found that the rate of pregnancies after the legislation was just as high as it was before (around one-third were successful). However, the frequency of twin pregnancies fell from 23% to less than 6%. Transferring a single embryo can still result in twins if one embryo splits naturally into two.

Two studies from US fertility clinics mirrored the Swedish results. When otherwise healthy women were offered the choice of having one embryo implanted instead of two, pregnancy rates remained just as high (over 70%).

Researchers hope that the data, which echo that emerging from a number of other studies, will encourage more clinics to favour single embryo transfers. In women aged over 37 years, or with previous experience of failed IVF, however, it may still make sense to transfer more than one embryo. The risk of multiple births is much lower in these groups.

Patient opposition

Many countries other than Sweden are already encouraging a limit to the number of embryos transferred. Last month, the ASRM released new guidelines advising US clinics to transfer no more than two embryos to women under 35.

However, one of the biggest obstacles to the widespread adoption of single embryo transfer is that patients in the United States and many other countries pay for their own treatment, which often costs over $10,000 for a single IVF cycle.

Wanting to maximize their chances of success, patients tend to favour the transfer of multiple embryos in each cycle; and clinics support the practice because they believe it will increase the pregnancy rates, which they publish to attract patients.

To overcome this perception, researchers say there is a need to educate patients about the new data and about the health risks associated with twins. "The challenge is to get people to accept it," says Marius Meintjes of Presbyterian Hospital in Dallas, Texas and author of one of the studies.