Now, a new study of 500 babies adds to the evidence that it might be worth keeping away from that tub of peanut butter if you’re pregnant. The study found a strong link between the mothers saying they’d eaten peanuts in pregnancy, and the babies having positive skin-prick and blood tests for peanut allergy. Babies were three times as likely to have positive tests, if their mothers had eaten peanuts – and the more often the mother ate peanuts, the stronger the link.

There are a few things about this study that should give us pause, however. Firstly, the allergy tests used in the study can't tell us for certain whether the babies were allergic to peanuts. These tests can only show whether someone is "sensitized" to peanuts, meaning that their immune system has an abnormal response to the food. To confirm an allergy, the person would need to eat peanuts in a controlled environment to see if they have a true allergic response. This type of test isn't appropriate for babies, but the researchers hope to follow up with the children when they are older.

We also know that people don’t always recall their diets accurately, especially after a period of months. Finally, this type of study can show a link, but cannot prove cause and effect.

What you need to know. There’s still no firm evidence about whether eating peanuts in pregnancy can increase the chances of your child getting peanut allergy. But this latest study suggests there may be something to the theory.

—Anna Sayburn, patient editor, BMJ Group

Also see, Are you living peanut-free when you needn't be?

*links to PDF