NEW YORK (Reuters Health) - Babies born by in vitro fertilization (IVF) do not face an increased risk of birth defects, nor are they at greater risk of being smaller than normal, according to a study conducted in Japan.
But the researchers did find that women pregnant via IVF were more likely than those who conceived naturally to develop a pregnancy complication called placenta previa, in which the placenta blocks the opening to the birth canal.
Some studies comparing babies born through IVF and those conceived naturally have found worse outcomes for the IVF infants, including higher rates of birth defects and greater likelihood of low birth weight, Mai Fujii of the World Health Organization in Geneva and her colleagues note in their report.
But the authors of a review of the best available data on IVF outcomes published in 2005 concluded that the risks of IVF compared with other fertility boosting methods, such as drugs to stimulate egg production or artificial insemination, are “unknown,” Fujii and her team add.
In the current study, the researchers compared nearly 54,000 naturally conceived single babies with about 1,400 single babies born via IVF; the sample represented 6 percent of all babies born in Japan in 2006.
Just 23 of the IVF babies died as newborns, such a small number that the researchers were unable to gauge whether or not IVF increased infant death risk. About one in five IVF babies were low birth weight, compared to about one in six naturally conceived babies (the control group), but the difference was no longer statistically significant after the researchers adjusted for mother’s age, a baby’s gestational age at birth, and other factors.
About 2 percent of both the IVF babies and the control group infants had birth defects. While there is some evidence that IVF is linked to certain types of birth defects, the researchers note, the current study did not include specific information on the malformations infants had.
Both groups of babies were at similar risk of being born small for gestational age, while the ratio of boys to girls born was the same in the IVF and the control group.
These findings offer no evidence that IVF babies are more likely to have problems than naturally conceived infants, the researchers say, but they note that the small number of infant deaths and birth defects means they can’t rule out “small to moderate increases” in these risks.
However, 5 percent of women who became pregnant via IVF developed placenta previa, compared to 1.5 percent of the women who conceived naturally.
Placenta previa is a complication that occurs in the second or third trimester of pregnancy, which can lead to heavy vaginal bleeding and interfere with the birth process. According to the American College of Obstetricians and Gynecologists, placenta previa occurs in 1 in 200 women. It is more common in women who have had more than one child, have had a cesarean section, have had surgery on the uterus, and who are pregnant with twins or triplets.
SOURCE: Fertility and Sterility, online February 1, 2010.
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