Pregnant women are being advised to avoid insect repellent after a study found a link to an increasingly common birth defect.

European researchers have found an association between expectant moms who used the repellent in the earliest phase of pregnancy and an increased rate of a condition known as hypospadias, which occurs when the opening of the penis — the urethra — is on the underside of the penis, instead of the top.

The condition, which often requires corrective surgery, affects 1-2 boys in every 500 births.

"This particular defect of the male urethra is quite common, and has been linked to environmental sources as well as genetic problems," Chris Winder, a University of New South Wales Professor of Toxicology and Occupational Health in Australia said.

"Here is more evidence that pregnant mothers, or mothers planning pregnancy, should limit their exposure to chemicals such as insect repellents," he added.

Click here to read more from news.com.au.