A 38-week pregnant woman reports bright red vaginal bleeding without pain. What condition may she be experiencing?

The presence of bright red vaginal bleeding without pain at 38 weeks of pregnancy is indicative of placenta previa. This condition occurs when the placenta partially or completely covers the cervix, leading to bleeding as the cervix begins to efface and dilate as the body prepares for labor. The absence of pain is a key feature that distinguishes this condition from others, such as abruptio placentae, which typically presents with painful bleeding due to the premature separation of the placenta from the uterine wall.

Gestational diabetes is primarily characterized by abnormal glucose metabolism and does not typically present with vaginal bleeding. Similarly, a threatened miscarriage usually presents with cramping or pain along with bleeding, which makes it less likely in this scenario. The characteristics of the bleeding (bright red, painless, and occurring late in pregnancy) strongly suggest that the woman is experiencing placenta previa.