A recent major Swedish study showed that in-vitro fertilization (IVF) is almost as effective for women who received only one embryo as women who received two embryos. The study also revealed that in doing so, the risk of giving birth to twins was minimized.

IVF is a 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.

In the world's largest controlled study, scientists at the Sahlgrenska Academy at Göteborg University in Sweden 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,’ said Prof. Christina Bergh and specialist physician Dr. Ann Thurin, who were in charge of the study.

The major benefit noted was 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,’ said 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,’ Bergh said.

The studies findings are published in the Dec. 2. 2004 edition of The New England Journal of Medicine