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 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 for babies born with the help of technology.
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 were to be reported Friday 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, IVF or in vitro (lab dish) fertilization, and more advanced methods like injecting a single sperm into an egg to create an embryo.
As many as 1 to 2 percent of births in the United States and Canada are due to such techniques. They already are known to raise the raise the risk of premature birth and other complications.
But studies have been divided over whether they increase the likelihood of birth defects. A recent scientific review concluded there is some added risk, but that most studies have been too small or flawed to be conclusive.
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.
Researchers studied 61,208 births in Ontario during 2005, including 1,394 that resulted from fertility treatments. They looked at rates of birth defects and adjusted estimates of risk to reflect differences in the mothers' ages, whether they smoked, the gender of the babies, birth complications and other factors.
Nearly 3 percent of ART babies had a birth defect versus just under 2 percent for babies conceived naturally. That translated to a 58 percent greater risk. The chances of a defect rose as the complexity of reproductive help did -- they were highest for IVF and lowest for simply giving medications to spur a woman's ovaries to make more eggs.
The biggest difference was seen in the rate of gastrointestinal problems, such as defects in the abdominal wall or organs not in the right place. Babies conceived through reproductive technology were nearly nine times more likely to have such problems -- one in 200 births versus six per 10,000 for the others.
However, "it's still pretty uncommon," said lead researcher Darine El-Chaar of the University of Ottawa.
The chance of cardiovascular defects was more than twice as high -- 90 per 10,000 babies conceived through ART versus 40 among those conceived naturally. Defects like malformed limbs also were slightly more common, but not facial defects like cleft palate or problems like spina bifida.
The bottom line: "I don't think women should worry about it," said Dr. Nancy Chescheir, obstetrics chief at Vanderbilt Medical Center, who had no role in the study.
The higher rates seen in this study are no worse than the 3 percent to 4 percent rates usually seen in the general population; the Canadians may have been healthier in general, she said.
Green said the risks are "not overpowering, but they're not insignificant."
The researchers note that people who have trouble conceiving also may have underlying genetic or health factors that could partly account for the higher rates of birth defects.
"We think this should become part of counseling couples that are infertile," especially that the degree of manipulating egg and sperm may affect the risk of defects, El-Chaar said.
