If you are not allergic to peanuts, there is no reason to avoid peanuts when pregnant or nursing.
According to some estimates, 8 percent of all children in the US have at least one identified food allergy. The peanut allergy is responsible for about one-fourth of those food allergies.
Women are concerned that eating peanuts while pregnant or nursing can cause the allergy to develop and for good reason. As recent as the year 2000, the American Academy of Pediatrics Committee on Nutrition recommended avoiding peanuts in the diet of lactating mothers. But all that is changing! Studies done more recently indicate that the OPPOSITE is true. Women who eat peanuts more often have a lower likelihood of having a child with a peanut allergy than women who rarely eat peanuts (defined as greater than five times per month verses less than once a month).
Of course, if you have a personal history of peanut allergy, then continue avoiding them.