Insect repellent use in early pregnancy linked to birth defect risk

The use of insect repellent during the first three months of pregnancy may boost the risk of the penile birth defect hypospadias, suggests research published online today.

The condition is thought to affect around one to two male births in every 500. But despite its prevalence, relatively little is known about the environmental risk factors for hypospadias, although it has been variously associated with low birthweight, a history of stillbirth, older mothers, poor fertility and smoking, among other things.

The researchers base their findings on 471 babies with the condition, who were born between January 1997 and September 1998 and referred to surgeons in the South East of England.

The researchers also included 490 randomly selected babies born during the same period to act as a comparison group.

The mothers of all the babies were quizzed about their lifestyles and certain environmental factors, including the use of insect repellents and biocides, such as pesticides or weedkillers, during pregnancy.

Exposure was scored from zero to eight to create a total biocide score, based on adding up positive responses to questions, such as living within a mile of a field used for agriculture; use of garden pesticides; use of fly strips or sprays/ant powder/rat poison; use of insect spray on plants; flea treatment of pets; and use of nit shampoo.

Individual biocides did not seem to be associated with an increased risk of hypospadias, but use of several biocides was associated with a 73% increased risk.

After taking account of factors likely to influence the results, the authors found that use of insect repellents during the first three months of pregnancy was associated with an 81% increased risk of hypospadias.

Insect repellents can contain N,N-diethyl-m-toluamide also known as DEET, permethrin, or other products. High doses of DEET are throught to be harmful, and the chemical can cross the placenta and enter the bloodstream of the developing fetus, say the authors.

But they caution that their study did not look specifically at the type, content, and frequency of use of insect repellents, and this should be investigated further before firm conclusions can be drawn.

The research is published in Occupational and Environmental Medicine (Online First Occup Environ Med 2009; doi 10.1136/oem.2009.047373)