One embryo as good as two to maximize the chance of pregnancy

Dec 3 2004

Nearly as many women who received only one embryo at a time gave birth as women who received two embryos. At the same time the risk of giving birth to twins is minimized. These are the findings of a major study from the Sahlgrenska Academy, at Göteborg University in Sweden.

In-vitro fertilization, IVF, is a successful method to help childless couples to become parents. To maximize the chance of pregnancy, physicians have generally reintroduced more than one embryo. This has led to a considerably larger proportion of multiple births compared with spontaneous pregnancies. Multiple birth means two or more children in the same pregnancy, most often twins. Expecting more than one child entails greater risk. These children are often born prematurely and often have low birth weight. To reduce the number of pregnancies with more than one child, the Swedish National Board of Health and Welfare recommends that only one embryo be transferred at a time.

In the world's largest controlled study, scientists at the Sahgrenska Academy in Gothenburg have compared deliveries in two groups of women who underwent IVF. Half of the women first had one embryo transferred. If it did not develop, they received a second embryo that had been kept frozen until it was reintroduced. The other half of the women received two embryos from the beginning. The study comprised 661 women under the age of 36 from 11 clinics in Scandinavia.

"The results show that there were nearly as many deliveries in both groups: 42.9 percent of the women in the two-embryo group gave birth, compared with 38.8 percent of the single-embryo group," says Professor Christina Bergh and specialist physician Ann Thurin, who were in charge of the study.

The great benefit is that the proportion of deliveries with twins or more siblings was minimal in the group of women who received one embryo at a time.

"In the single-embryo group, 0.8 percent of the deliveries were multiple, compared with 33.1 percent of deliveries in the two-embryo group," say the researchers.

In Scandinavia single-embryo reintroductions are already a routine at many clinics. "The study findings will hopefully hasten developments toward the introduction of one embryo at a time in other parts of the world," says Christina Bergh.

The studies findings are being published on December 2. 2004, in the prestigious American medical journal The New England Journal of Medicine.

Brief facts about IVF/In-Vitro Fertilization In IVF eggs are taken from the woman's ovaries. The eggs are placed in a nutrient solution together with sperm. Those eggs that become fertilized can be returned to the woman and develop there into a fetus. Embryos of good quality can be preserved frozen and be transferred to the woman in the same way, after thawing.

The world's first successful IVF was carried out in the United Kingdom in 1978, and since then around one million IVF children have been born around the world. Scandinavia's first successful IVF was performed at Sahlgrenska Hospital in Gothenburg in 1982. In Sweden some 2,500 children per year are born as a result of successful IVF-treatment.