Source: Michelle Robinson, Sunday Star Times

A common fertility drug could be contributing to shorter boys.

A study by Auckland University's Liggins Institute found boys conceived using the drug clomiphene grew up shorter than those conceived without it but girls were barely affected.

The drug is commonly given as a pill or by injection in fertility treatment to cause ovarian stimulation.

The boys in the study were on average three centimetres shorter than their counterparts.

"They're not dwarves or anything," research scientist and Fertility Associates operations director John Peek, left, said.

The research, part of a six-year study of children aged four to 10 and the effects of IVF and fertility treatment on growth, is being presented at the Fertility Society of Australia's conference next week.

Earlier research found girls conceived under IVF were taller than others their age, but the most noticeable difference in boys was for those conceived with the use of clomiphene, Peek said.

"The next question is why?" he said, adding that it was not known whether the difference was caused by the parents' infertility, or the drugs to overcome it.

One theory looked at epigenetics – the study of how environment and choices could affect the genetic code.

"We're not sure what's going on here."

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Related information
- IVF-lings.co.nz, the website for children born from IVF.  It will explain and help you how you came to be and what IVF is all about.