Pregnancy can interfere with a woman's sugar levels, making her temporarily diabetic. Gestational diabetes is pretty common -- occurring in 2-14 percent of women. Untreated gestational diabetes can lead to excessively big babies with consequent difficult delivery, and, rarely, stillbirth.
With good control of blood sugar levels and proper medical care, babies of gestational diabetic mothers usually do very well. Gestational diabetes is more likely for women with a family history of diabetes, those who are overweight, and older moms.
Since most mothers-to-be who develop gestational diabetes don't have trouble with their blood sugar until late in pregnancy, the test isn't routinely taken until after 24 weeks. Women at increased risk for diabetes may benefit from first trimester testing as well.