Subchorionic Haematoma

Subchorionic haematoma is a collection of blood between the chorionic membrane and the uterine wall, caused by partial separation of the chorion from the decidua. It is found in about 1 to 3 percent of first trimester scans and is a common cause of bleeding with a living embryo. Most resolve without harm, but large collections raise the risk of miscarriage, abruption and preterm birth.

• Risk factors: previous miscarriage, uterine anomaly, assisted reproduction, anticoagulant use.
• Size matters: a collection above 20 percent of the sac size carries more risk.
• Most disappear by 20 weeks.

Women have painless vaginal bleeding of variable amount, often brown or red, sometimes with light cramping. Many have no symptoms and the haematoma is a scan finding.

• Closed cervical os.
• Uterus size matches dates.
• Differential diagnosis: threatened miscarriage, ectopic pregnancy, cervical polyp, molar pregnancy, low implantation of the sac.
• Complications: miscarriage, anaemia, infection, placental abruption, preterm labour, premature rupture of membranes.

The diagnosis is made on ultrasound.

• Transvaginal ultrasound: crescent shaped hypoechoic or anechoic collection adjacent to the gestational sac, with measurement of length, width and depth and a comparison with sac size.
• Confirm a live embryo with cardiac activity.
• Haemoglobin, blood group and Rhesus status.
• Repeat scan at 2 weeks to follow size.

The principle is expectant management with monitoring and treatment of anaemia and infection.

• Supportive: reassure that most resolve; avoid heavy lifting and intercourse while bleeding; bed rest is not needed; increase oral fluids.
• Pharmacological: paracetamol 1 g oral 6-hourly as needed (maximum 4 g in 24 hours); for bleeding with at least one previous miscarriage, give micronised progesterone 400 mg vaginally twice daily until 16 weeks; ferrous sulphate 200 mg oral 8-hourly if haemoglobin is below 11 g/dL; folic acid 400 micrograms oral daily; stop aspirin or enoxaparin only on specialist advice.
• Procedures: none.
• Special groups: Rhesus negative women with heavy bleeding give anti-D immunoglobulin 250 IU IM within 72 hours; women on enoxaparin 40 mg subcutaneous daily for a thrombotic indication continue it with close review.
• Red flags: heavy bleeding, passage of clots, severe pain, fever above 38 degrees Celsius, offensive discharge.
• Follow-up: ultrasound at 2 weeks and at the 20 week scan for placental position; growth scans at 28 and 32 weeks if large; antenatal care.