The children conceived with the help of fertility drugs were nearly an inch shorter than the others, although still within the normal range, even with differences in their parents' height taken into account. Parental height is considered the key factor in determining a child's height.
The height difference was greater in boys, who were more than an inch shorter on average than naturally conceived boys.
There was no significant difference in general physical health between the two groups of children.
The authors speculated that the height difference may be due to something that happens around the point of conception. They suggested it could be caused by "imprinting" variations -- changes in the way genes are expressed, which could be related to the process of ovarian stimulation. The appropriate expression of genes is important in normal development.
Other experts greeted the study findings with caution.
Dr. Edward Illions, an associate professor of obstetrics and gynecology at Albert Einstein College of Medicine and a reproductive endocrinologist at Montefiore Institute for Reproductive Medicine in Hartsdale, N.Y., said any number of mechanisms, including the act of stimulation, could affect imprinting.
Illions also expressed concern with the study's limitations. "The researchers don't tell us which particular drugs the women were on, what stimulation protocols were used or the number of treatment cycles rendered to these patients," he said.
Dr. David Cohen, chief of reproductive endocrinology and infertility at the University of Chicago, said researchers n
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