Many women are surprised to find out just how far along they are in their pregnancies when they see their obstetrician for the first time. Bleeding during the first trimester is not uncommon, and many women think they are actually having a period. Subchorionic hemorrhage is not the result of anything the mother has done. It is suspected that subchorionic hemorrhage occurs from the rapid growth of the gestational sac.
Ultrasound
First trimester ultrasound is done for early pregnancy bleeding or spotting. It is often done to confirm the viability of an early pregnancy and to acquire an accurate due date. Many things are seen on the first trimester ultrasound, most of them normal. Subchorionic hemorrhages are often seen during this ultrasound. While it is considered to be an abnormality, it is seen in many pregnancies and often is of no consequence.
Also known as a subchorionic hematoma, it is often seen using transvaginal sonography. Most subchorionic hemorrhages are small and will not have an effect on the pregnancy. They generally clear up by the second trimester. Subchorionic hemorrhage is a possible cause for vaginal bleeding, which occurs in 25% pregnancies according to Avneesh Chhabra, M.D. (eMedicine: Subchorionic Hemorrhage).
Using ultrasound, subchorionic hemorrhages are usually seen as an anechoic (black) area. Some hematomas may look the same as the placenta (isoechoic) and may not be seen. Larger hematomas are more likely to contribute to a poor outcome and may cause bleeding throughout the duration of the pregnancy.
Ultrasound does not always show the presence of a subchorionic hemorrhage, especially when vaginal bleeding is present. This is because the blood may not remain contained in the subchorionic space around the gestational sac while it flows into the vaginal canal. If no fluid collection is present, it cannot be seen on ultrasound. According to Dr. Chhabra, subchorionic hemorrhages are associated with 4-33% of miscarriages. This does not necessarily mean that they are the cause or are associated with the cause of miscarriage, but that they are present.
Third Trimester
Subchorionic hemorrhages generally clear up in the first trimester, and may be a sign of something more serious late in the pregnancy. Subchorionic hemorrhages in the third trimester may result in placental abruption, although this is not common. Placental abruption is the tearing of the placenta from the uterine wall. It is accompanied by abdominal pain and vaginal bleeding.
Treatment
Subchorionic hemorrhages are generally followed with serial ultrasounds. Depending on the extent of the hemorrhage, the patient may be asked to abstain from sexual intercourse and strenuous activity. If the hemorrhage is large, increasing in size, or is associated with a multiple pregnancy, bed rest may be prescribed. Most often, the subchorionic hemorrhage resolves, bleeding stops, and the pregnancy continues without complication.
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