Women who put on even a little weight after a first pregnancy have an increased chance of experiencing complications in a second one. Researchers have found that a gain of one to two body mass index (BMI) units increased women's risk for gestational diabetes, hypertension and large-for-gestational-age babies by 20 percent to 40 percent.
A BMI of 25 is overweight; 30 or above is obese. A 5-foot-5-inch woman who weighs 138 has a "healthy" BMI of 23. Gaining as few as 7 pounds between pregnancies would boost her BMI to 24 and her risk for gestational diabetes by 30 percent--even though she hadn't gained enough to be considered overweight.