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, compar