A subchorionic hemorrhage is caused when blood collects between the chorionic membrane (a membrane that develops around a fertilized egg) and the wall of the uterus. If blood leaks through the cervix, this subchorionic bleeding may result in vaginal bleeding. However, not all bleeding occurs due to subchorionic hemorrhage.
For women who are pregnant, vaginal bleeding is a fairly common occurrence, and one that is not usually dangerous. It can, of course, be very distressing – but around 25% of women experience some form of it during their first trimester of pregnancy, so this isn’t necessarily anything to worry about. However, subchorionic hemorrhage is potentially a dangerous complication of pregnancy, so vaginal bleeding should never be ignored.
Around 1.3% of pregnant women experience subchorionic bleeding, but only 20% of women who experience any type of vaginal bleeding during their first trimester will develop subchorionic hemorrhage. Because of this risk, it’s important to consult your doctor if you experience any bleeding at all even if it is unlikely that it is dangerous.
Severe subchorionic bleeding can lead to rupture of the subchorionic membrane, and in the worst cases may lead to a miscarriage. Of women who develop subchorionic hemorrhage, around 9% miscarry. The risk increases somewhat in women over 35.