Mothers Who Use Fertility Drugs May Have Shorter Kids

(Image credit: <a href=''>Boy checking height</a> via Shutterstock)

Children conceived through use of fertility drugs may not grow quite as tall as other kids, a new study from Australia suggests.

In the study, boys whose mothers used fertility drugs were on average 1 inch (3 centimeters) shorter at ages 3 to 10, compared with boys of mothers who did not use the drugs.

While girls whose mothers who used fertility drugs also tended to be shorter than other kids, the findings were not as strong and could have been due to chance.

It's possible it wasn't the drugs, but something related to the parent's fertility problems that influenced the children's height, but the researchers found this was not the case. Children whose parents who used fertility drugs were shorter than children whose parents who had trouble having kids, but eventually conceived without taking fertility drugs.

The results were unexpected, the researchers said. Previous studies have found that children conceived using in vitro fertilization, which also uses fertility drugs, are taller than naturally-conceived children.

Because they study was small, further research is needed to confirm the findings. Additional studies are also needed to see whether the height difference persists into adulthood, the researchers said.

Other experts are not convinced by the findings. Dr. Avner Hershlag, chief of the Center For Human Reproduction at the North Shore Long Island Jewish Health System in Manhasset, N.Y., urged women considering fertility treatment not to resist treatment because of this study's results. "There is not solid evidence right now" of the link between fertility drug use and short stature in children, Hershlag said.

Effects of fertility drugs

While several studies have examined the effects of fertility treatments such as in vitro fertilization on children, few studies have examined the effects of fertility drug use alone.

In the new study, Wayne Cut?eld, of the University of Auckland, and colleagues analyzed information from 84 children whose mothers underwent ovarian stimulation with fertility drugs. They compared this group with 214 children whose parents were fertile and conceived naturally, and 54 children whose parents took more than 12 months to conceive, but eventually did so without treatments.

The average age of children in the study was 7.5.

The link between a shorter stature in children and use of fertility drugs held even after the researchers took into account factors that affect the height of children, such as the height and weight of the parents.

It's possible that ovarian stimulation with fertility drugs leads to alterations in certain genes in the embryo that result in developmental changes, the researchers said.

Complex trait

However, height is a very complex trait, and is influenced by many factors, including the environment a child grows up in, and the food he or she eats, Hershlag said.

"To me, that would be much more important than a drug given before conception," Hershlag said.

The researchers tried to account for family factors that could influence height by limiting their study to children of European descent, from families living in high socioeconomic communities. But Hershlag pointed out even siblings from the same family have different heights.

In addition, mothers in the study received different fertility treatments — some received the oral drug clomiphene, other received injections of follicle-stimulating hormone, and some received both treatments at once. This "hodgepodge" of treatments makes it hard to draw firm conclusions from the study, Hershlag said.

The study was published online July 9 in the journal Human Reproduction.

Pass it on:  In a new study from Australia, boys whose mothers used fertility drugs were about one inch shorter than boys whose mothers did not use fertility drugs.

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Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.