SAN DIEGO -- More than 30 years after the world greeted its first "test tube" baby with a mixture of awe, elation and concern, researchers say they are finding only a few medical differences between those children and kids conceived the traditional way.
More than 3 million children have been born worldwide as a result of assisted reproductive technology, and injecting sperm into an egg outside the human body now accounts for about 4 percent of live births, researchers reported Sunday at the annual meeting of the American Association for the Advancement of Science.
Most assisted-reproduction children are healthy and normal, according to researchers who have studied them.
Some of the children do face an increased risk of birth defects, such as neural tube defects, and of low birth weight, which is associated with obesity, hypertension and type II diabetes later in life, the researchers said.
"Overall, these children do well," said Andre Van Steirteghem of the Brussels Free University Center for Reproductive Medicine in Belgium. "It is a reassuring message, but we must continue to follow up."
Carmen Sapienza, a geneticist at the Temple University School of Medicine in Philadelphia, noted that few test tube children are older than 30, so it's not known whether they will be obese or have hypertension or other health problems at age 50 or beyond.
Sapienza said researchers found differences in 5 to 10 percent of chromosomes between assisted-reproduction children and other kids.
It's unclear, however, whether the differences result from assisted reproduction or other factors, perhaps ones that caused the couple's infertility in the first place.
Only a small fraction of the assisted-reproduction children were outside the normal range of gene expression, Sapienza reported.
"However, because some of the genes found to be affected are involved in the development of fat tissue and the metabolism of glucose, it will be interesting to monitor these children long-term to determine whether they have higher rates of obesity or diabetes."
Van Steirteghem said: "There are genetic causes of infertility that you can bypass now. But this may mean that the next generation will be infertile, and that is something that all clinics should mention."