Dr. Tim Savage, a pediatrician at The Liggins Institute at the University of Auckland, New Zealand, said the study involved 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 ages from 3-10. 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 1 inch, shorter than the other children, Savage said.
In their statistical analysis, the researchers individually corrected the height of each child for the parents' height, because parents' height is the most important determining factor of a child's height, Savage said.
The height difference was more pronounced in boys than girls. Boys in the fertility drug group were 3 centimeters, or just more than 1 inch, shorter on average than the naturally conceived boys, Savage said.
The cause of the slightly shorter stature is unclear, as is whether the children catch up in stature when they reach their full adult height, Savage told The Endocrine Society's 94th annual meeting in Houston.