Repellents and insecticides linked to birth defects in baby boys

If you're pregnant, you've probably received no shortage of advice about things to avoid. No soft cheeses, deli meats, or raw eggs. Be careful about fish that might contain mercury. Cut out or cut down on alcohol. It's natural to want to do everything you can to protect your baby, but it can also be difficult working out just how big the risks are that you're trying to avoid.

New research from England suggests that there's something else to be careful about during pregnancy: insect repellents and insecticides. Researchers looked at 471 baby boys born with a malformation called hypospadias, where the opening of the penis appears on the underside, rather than the tip. (Surgery can correct the problem in most cases, although no surgical procedure is completely without risk.)

The boys' mothers were asked about their lifestyles. Compared with the mothers of healthy babies, mothers of boys with hypospadias were more likely to have used insect repellents during the first trimester of pregnancy.

The researchers also looked at whether insecticides used in gardening, farming, or pest control might be linked to birth defects. They looked at whether women lived near farmland, used pesticides in the garden, used fly sprays or ant powder, treated pets for fleas, or used nit shampoo. No single one of these things was linked to a higher risk, but women who had a combination of several were more likely to have a son with hypospadias.

The new study can't prove that insect repellents or insecticides are the cause of birth defects. We only know there's a link. Another problem with the study is that the researchers didn't ask about the specific products women used, so it's impossible to say which individual repellents might be linked to the increased risk. Active ingredients in repellents include DEET and permethrin, while natural repellents may contain essential oils, like citronella or eucalyptus.

The researchers say that more research needs to be done on insect repellents before we can draw firm conclusions. There are probably several things that increase the risk of genital defects in boys, with smoking being another likely factor. It's difficult to know just how big a part repellents or insecticides might play.

Research done last year suggested that taking folic acid supplements might help protect your baby from hypospadias. Folic acid also helps prevent major birth defects, like spina bifida. A 400 microgram folic acid supplement is recommended to all women trying for a baby, from the time when you stop using contraception up to week 12 of your pregnancy.

What you need to know. There hasn't been much research looking at whether individual insect repellents are safe during pregnancy. There may be times when you need to use them; for example, if you're travelling in a malarial area. Talk with your doctor if you're in any doubt.

—Philip Wilson, patient editor, BMJ Group

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