A new study is the latest evidence that the ‘first-line’ strategy for preventing gestational diabetes mellitus isn’t working. Over the past five years, more than 5,000 pregnant women took part in clinical trials focused on limiting weight gain in order to prevent gestational diabetes. The moms-to-be improved their diet quality, ate less, and increased their physical activity. They also developed gestational diabetes at about the same rates as the women who didn’t change their diet or activity levels.