The risks of being overweight while pregnant are well known, but a new study says that gaining just a few pounds a year in the years before pregnancy—even if that weight gain doesn't push you into unhealthy territory—sharply raises the risk of gestational diabetes. "Women with small weight gains within the healthy BMI range doubled their risk of gestational diabetes compared to women whose weight remained stable," says researcher Akilew Adane, with "small" being defined as a gain of 1.5% to 2.5% of body weight a year. Adane gives this example: A 5-foot-5-inch woman weighing 132 pounds (a healthy BMI) doubles her risk if she gains 2.5 pounds a year, or about 2% of her body weight, for seven years. When the gain was over 2.5%, the women had 2.7 times the risk.
Gestational diabetes can cause birth complications and lead to long-term health problems for mother and baby. In the study, published in Diabetes Research and Clinical Practice, the researchers followed more than 3,000 Australian women from 1996, when they were ages 18 to 23. Participants answered questions about their health and lifestyle. The team suspects those early adults who gained weight "may experience a modest progressive insulin resistance, which is further exacerbated by pregnancy, even though their weight is still within the normal range." They see weight gain prevention during these pre-pregnancy years "to be the main strategy to prevent the incidence" of gestational diabetes. (The jury is in on exercising while pregnant.)