Study shows children conceived with fertility drugs are shorter than their peers
Results of a new study designed and supervised by Professor Wayne Cutfield, Director of the Liggins Institute, and funded by a grant from New Zealand’s National Research Centre for Growth and Development were presented this week at The Endocrine Society’s 94th Annual Meeting in Houston.
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, the study finds.
“Reassuringly, these children remained well within the normal height range for both their sex and age,” said Dr Tim Savage, a pediatrician and clinical research fellow at The University of Auckland’s Liggins Institute, who conducted the study as part of his PhD research.
The cause of the slightly shorter stature of fertility drug–conceived children is unclear, Savage said. Also unknown is whether or not these children catch up in stature when they reach their full adult height.
Because some studies have found that children conceived via in vitro fertilization (IVF) 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 IVF. Although ovarian-stimulating drugs are part of IVF (which also includes fertilisation 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. In order to optimise the 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 explained.
As a group, the fertility drug–conceived children were an average of 2 centimeters, shorter than the other children, considering their age, sex, and parents’ height.
The height difference was more pronounced in boys than girls, with boys in the fertility drug group on average 3 centimeters shorter than the naturally conceived boys. The reason for the height difference has yet to be elucidated and requires further investigation.
There were no important differences in general physical health between groups: the fertility drug–conceived children had a healthy weight and percentage body fat as well as excellent cholesterol and blood glucose 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.”