Chorionic hematoma is the pooling of blood (hematoma

Hematoma

A hematoma, or haematoma, is a localized collection of blood outside the blood vessels, usually in liquid form within the tissue. This distinguishes it from an ecchymosis, which is the spread of blood under the skin in a thin layer, commonly called a bruise...

) between the chorion

Chorion

The chorion is one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes...

, a membrane surrounding the embryo

Embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

, and the uterine wall

Uterus

The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...

. With an incidence of 3.1% of all pregnancies, it is the most common sonographic abnormality

Medical ultrasonography

Diagnostic sonography is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions...

 and the most common cause of first trimester bleeding

First trimester bleeding

In obstetrics, first trimester bleeding, is bleeding from the vagina during pregnancy in the first trimester .It is a common occurrence and estimated to occur in approximately 25% of all pregnancies....

.

Cause and diagnosis

Chorionic hematomas can be caused by the separation of the chorion from the endometrium

Endometrium

-Function:The endometrium is the innermost glandular layer and functions as a lining for the uterus, preventing adhesions between the opposed walls of the myometrium, thereby maintaining the patency of the uterine cavity. During the menstrual cycle or estrous cycle, the endometrium grows to a...

 (inner membrane of the uterus). Hematomas are classified by their location between tissue layers:

• Subchorionic hematomas, the most common type, are between the chorion and endometrium.
• Retroplacental hematomas are entirely behind the placenta and not touching the gestational sac.
• Subamniotic or preplacental hematomas are contained within amnion and chorion. Rare.

Most patients with a small subchorionic hematoma are asymptomatic. Symptoms include vaginal bleeding

Vaginal bleeding

Vaginal bleeding refers to bleeding in females that is either a physiologic response during the non-conceptional menstrual cycle or caused by hormonal or organic problems of the reproductive system. Vaginal bleeding may occur at any age, but always needs investigation when encountered in female...

, abdominal pain

Abdominal pain

Abdominal pain can be one of the symptoms associated with transient disorders or serious disease. Making a definitive diagnosis of the cause of abdominal pain can be difficult, because many diseases can result in this symptom. Abdominal pain is a common problem...

, premature labor and threatened abortion.

Ultrasonography is the preferred method of diagnosis. A chorionic hematoma appears on ultrasound as a hypoechoic crescent adjacent to the gestational sac

Gestational sac

The gestational sac is the only available intrauterine structure that can be used to determine if an intrauterine pregnancy exists, until the embryo is identified....

. The hematoma is considered small if it is under 20% of the size of the sac and large if it is over 50%.

Prognosis and treatment

Chorionic hematomas are associated with an increased risk of miscarriage

Miscarriage

Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving independently, generally defined in humans at prior to 20 weeks of gestation...

, 9.3% for patients with a live fetus and hematoma identified in the first trimester according to a study by Bennett et al, but most regress naturally and do not worsen the patient's prognosis. There is no known therapeutic intervention.