SAN FRANCISCO -- Babies conceived through fertility treatments have higher rates of birth defects, but the overall risk is so small that it should not keep couples from having children this way, doctors are reporting.
The news comes from a study of more than 61,000 births in Canada, the largest ever done on this subject in North America.
"What's important and reassuring is that the absolute risks are still low," at less than 3 percent of all births, said one of the study's leaders, Dr. Mark Walker of the University of Ottawa.
Even so, the risks of certain defects were startlingly high .
Couples who want to lower the risk should have only one or two embryos implanted at a time, specialists said. The danger of defects from twin, triplet, and other multiple births is far greater than any risk posed by the fertility treatments themselves.
Results of the study are to be reported today at a meeting of the Society for Maternal-Fetal Medicine in San Francisco.
More than 1 million babies worldwide have been born through assisted reproductive technology, or ART.
This includes induced ovulation, artificial insemination, in vitro fertilization, and more advanced methods such as injecting a single sperm into an egg to create an embryo.
Up to 1 percent to 2 percent of births in the United States and Canada are results of such techniques. They already are known to raise the risk of premature birth and other complications.
The Canadian work is important because it's a large study and quantifies the risk of specific birth defects, "a first as far as I know," said Dr. Nancy Green, medical director of the March of Dimes.