br br A glucose screening test measures a woman’s blood glucose (sugar) level during pregnancy. But why do you need to worry about your blood sugar levels during pregnancy? Because of gestational diabetes (GDM). Gestational diabetes affects one in ten pregnant women, and usually begins between the 24th and 28th weeks of pregnancy, because the body is not producing enough insulin. While some women are at a higher risk, it is recommended that all women get tested during pregnancy (according to the American Congress of Obstetrics and Gynecologists).