Among children born full term, those conceived with the help of fertility drugs are slightly shorter than naturally conceived children but overall are physically healthy, a new study finds. Results of the study will be presented Saturday at The Endocrine Society's 94th Annual Meeting in Houston.
"Reassuringly, these children remained well within the normal height range for both their sex and age," said researcher Tim Savage, MD, a pediatrician and research fellow at The Liggins Institute, University of Auckland, in Auckland, New Zealand.
Because some studies have found that IVF-conceived children are taller than naturally conceived children, the authors aimed to determine whether there was a difference in height for children whose mothers used only fertility drugs, such as clomiphene (Clomid), without in vitro fertilization (IVF). Ovarian-stimulating fertility drugs are part of IVF, but IVF also includes fertilization and culture of embryos in a laboratory dish.
Successful use of ovarian stimulation alone is at least twice as common as IVF, accounting for about 5 percent of all live births in the developed world, Savage stated.
The researchers studied 84 children conceived with the help of fertility drugs alone and 258 children who were conceived naturally. All children were from a single-fetus, full-term pregnancy and ranged in age from 3 to 10 years. To optimize accuracy of the study, the researchers included only children who were born at full term and did not have a low birth weight, because children born small or prematurely have an increased risk of health problems, Savage said.
As a group, the fertility drug-conceived children were an average of 2 centimeters, or nearly an inch, shorter than the other children, considering their age and sex, Savage reported. In their statistical analysis, the researchers individually corrected the height of each child for their parents' height, because parents' height is the most important determining factor of a child's height, he explained.
When the groups were studied by sex, the height difference was more pronounced in boys than girls. Boys in the fertility drug group were 3 centimeters, or just more than an inch, shorter on average than the naturally conceived boys, according to Savage.
The cause of the slightly shorter stature of fertility drug-conceived children is unclear and requires further investigation, Savage said. Also unknown is whether these children catch up in stature when they reach their full adult height.
There were no important differences in general physical health between groups. Savage said the fertility drug-conceived children had a healthy weight and body fat percentage as well as excellent cholesterol and blood glucose (sugar) levels.
"Fertility treatment helps millions of couples to achieve their dream of becoming parents," Savage said. "It is important to continue research in this area in order to provide medical practitioners, parents and children with valuable information."
The study was designed and supervised by Wayne Cutfield, MD, director of The Liggins Institute, and was funded by a grant from New Zealand's National Research Centre for Growth and Development.