As with other forms of diabetes, gestational diabetes affects the way a woman's body uses glucose, or sugar, explains obstetrician and gynecologist Kyoko Peña-Robles with One Medical Group in San Francisco. "Pregnancy increases the body's need for insulin. If a woman's pancreas doesn't produce enough extra insulin, her blood glucose levels stay abnormally high," she states. "If there isn't enough insulin to carry sugar to the cells, or if the body stops responding to insulin, sugar builds up in the blood, resulting in gestational diabetes," she adds. Because untreated gestational diabetes can cause prenatal complications, such as an increased risk of preeclampsia and preterm labor, as well as a high birth weight at delivery, you'll be tested for it between your 24th and 28th week of pregnancy. If found, it can be treated with diet, exercise or, if necessary, with oral medications or insulin injections, states Dr. Peña-Robles.