Eating strawberries does not cause birth defects and strawberries are not bad for pregnant women.
In fact, eating strawberries is a good way to help prevent some birth defects. Strawberries contain folate, a B-complex vitamin that is important for prevention spina bifida, which is a neural tube defect. Spina bifida is a condition where the spinal vertebrae (back bones) don't completely enclose the spinal cord. It can cause a mild defect or be life-threatening for the baby.
Strawberries are also an excellent source of vitamin C, contain phytochemicals (natural plant chemicals) that may be good for your health. They're also low in calories.
The confusion about strawberries and birth defects is probably due to a list of the pesticide levels found on fruits and vegetables that was published by the Environmental Working Group. According to this study, strawberries rank high on a list of fruits and vegetables that contain pesticide residues. Pesticide exposure may increase the risk of birth defects, but that's typically due to occupational or environmental exposure to pesticides, not from foods.
All commercially grown strawberries contain low levels of pesticide residues unless they are grown organically. These levels have been determined to be safe, even for pregnant women. The Environmental Protection Agency suggests that to reduce your exposure to pesticides, you should wash or peel all fruits and vegetables before you eat them and purchase your produce from a variety of sources to reduce your exposure to pesticides.
The best way to reduce pesticide exposure is to buy organically grown strawberries, as well as other organic fruits and vegetables. Choosing organic produce will help prevent exposure to any residues because organically grown crops are not treated with synthetic pesticides.
There are some foods a pregnant woman should avoid, but strawberries aren't one of them. If you're pregnant, you should avoid raw milk products, soft cheese, raw fish and seafood, and certain types of fish that are high in mercury.
Centers for Disease Control and Prevention. "Spina Bifida - What You Should Know." Accessed February 9, 2012. http://www.cdc.gov/ncbddd/spinabifida/.
Thulstrup AM, Bonde JP. "Maternal occupational exposure and risk of specific birth defects." Occup Med (Lond). 2006 Dec;56(8):532-43.
United States Environmental Protection Agency. "Pesticides and Food: Healthy, Sensible Food Practices." Accessed February 9, 2012. http://www.epa.gov/pesticides/food/tips.htm.