Vaginal bleeding during pregnancy is not uncommon, but it's also not normal, says Chris A. Beard, a certified nurse-midwife in Portland, Oregon. It can indicate many things, depending on whether it's heavy or light, how long it lasts, what color it is, and at what point in the pregnancy it occurs. The color of the blood is also important -- blood that's bright red is usually more worrisome than blood that's brownish.
Call your doctor or midwife immediately if you have more than a dime-size spot of blood. Bleeding during pregnancy is a major warning sign of miscarriage, problems with the placenta, or preterm labor. Signs that bleeding is due to one of these serious conditions include heavy bleeding (similar to menstrual bleeding), bleeding in conjunction with cramps and/or fever, or bleeding and passing some tissue.
There are also less serious or benign causes for spotting and bleeding during pregnancy. Many women who spot go on to deliver healthy babies. However, even if you suspect that your spotting is not serious, you should still call your doctor.