About 25 percent of pregnant women have vaginal bleeding in the first half of pregnancy. If you have bleeding, your doctor may order an imaging study (ultrasound) to find the cause. The most common cause found on an ultrasound is bleeding that forms between the wall of your uterus and the sac that surrounds your placenta. Blood can leak into your uterus and come out through your vagina. This condition is called a subchorionic hemorrhage or hematoma (SCH). 
SCH occurs in about 2 percent of pregnancies. In most cases, SCH is not dangerous. It is one of many causes of bleeding or spotting during early pregnancy. Other causes include normal implantation bleeding and cervical changes. Sexual intercourse and infection can also cause bleeding. The major concern regarding any early vaginal bleeding is miscarriage. 
What Does SCH Mean for Your Pregnancy?
For most women with SCH, pregnancy will not be affected, but there is some cause for concern. How SCH affects pregnancy is a matter of some debate. SCH may increase the risk of miscarriage. It has also been linked to stillbirth, preterm labor, and placental abruption. Placental abruption is early separation of your placenta before birth. Some studies support these risks and some do not. [1-3]
A large study published in the journal Obstetrics & Gynecology followed over 1,000 women diagnosed with SCH. They found these women only has an increased risk for placental abruption and preterm labor. The risk for these conditions was small, under 5 percent.  Another study presented at the International Society of Ultrasound in Obstetrics and Gynecology followed 142 women diagnosed with SCH and found no increased risk for miscarriage. 
How SCH affects pregnancy may also depend on the size of the SCH and when it occurs during pregnancy. A small SCH that occurs early in the first trimester will usually reabsorb and cause no problems. A large SCH that occurs late in the first trimester or in the second trimester may push your placenta away from the wall of your uterus. This is could potentially result in loss of the pregnancy. 
What Happens if You Have SCH?
The cause of SCH is not known. You may be at higher risk if you had a pregnancy with in vitro fertilization (IVF). For many women the only sign is vaginal bleeding. Some women may also have cramping or pain. In any case, you should always let your doctor know about any vaginal bleeding. 
If SCH is diagnosed, treatment is similar to other causes of vaginal bleeding in pregnancy. You may be asked to rest more and avoid strenuous activity. You may be asked to avoid sexual activity. Some doctors may prescribe the hormone progesterone. Some studies show that progesterone lowers the risk of miscarriage. Your doctor will follow you more closely and repeat your ultrasound to see if your SCH is resolving. In most cases, it will. 
- Medscape, Subchorionic Hemorrhage Imaging.
- Medical News Today, What to know about subchorionic bleeding.
- Obstetrics & Gynecology, Ultrasound-Detected Subchorionic Hemorrhage and the Obstetric Implication.
- MDedge/ObGyn, Miscarriage risk is not increased with subchorionic hematoma.