Chorionic hematoma (also chorionic hemorrhage) is the pooling of blood (hematoma) between the chorion, a membrane surrounding the embryo, and the uterine wall. It occurs in about 3.1% of all pregnancies, it is the most common sonographic abnormality and the most common cause of first trimester bleeding.

Chorionic hematomas can be caused by the separation of the chorion from the endometrium (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, abdominal pain, 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. The hematoma is considered small if it is under 20% of the size of the sac and large if it is over 50%.

Obstetrical bleeding also known as obstetrical hemorrhage and maternal hemorrhage, refers to heavy bleeding during pregnancy, labor, or the postpartum period. Bleeding may be vaginal or less commonly but more dangerously, internal, into the abdominal cavity. Typically bleeding is related to the pregnancy itself, but some forms of bleeding are caused by other events.

The most frequent cause of maternal mortality worldwide is severe hemorrhage with 8.7 million cases occurring in 2015 and 83,000 of those events resulting in maternal death. Between 2003 and 2009, hemorrhage accounted for 27.1% of all maternal deaths globally

In ICD-10, early pregnancy bleeding (code O20.9) refers to obstetrical hemorrhage before 20 completed weeks of gestational age.

First trimester bleeding, is obstetrical hemorrhage in the first trimester (0 weeks-12 weeks of gestational age). First trimester bleeding is a common occurrence and estimated to occur in approximately 25% of all (clinically recognized) pregnancies.

Differential diagnosis of first trimester bleeding is as follows, with the mnemonic AGE IS Low (during first trimester):

- Abortion (spontaneous), also referred to as miscarriage. One study came to the result that the risk of miscarriage during the course of the pregnancy with just spotting during the first trimester was 9%, and with light bleeding 12%, compared to 12% in pregnancies without any first trimester bleeding. However, heavy first trimester bleeding was estimated to have a miscarriage risk of 24%.

- Gestational trophoblastic neoplasia

- Ectopic pregnancy, which implies a pregnancy outside the uterus, commonly in the fallopian tube, which may lead to bleeding internally that could be fatal if untreated. In cases where there is heavy bleeding and an obstetric ultrasonography assists in diagnosing a pregnancy of unknown location (no visible intrauterine pregnancy), it has been estimated that approximately 6% have an underlying ectopic pregnancy.

- Implantation bleeding

- Chorionic hematoma

- Spotting

- Lower GU tract causes

- Vaginal bleed

- Cervical bleed

Other causes of early pregnancy bleeding may include:

- Postcoital bleeding, which is vaginal bleeding after sexual intercourse that can be normal with pregnancy

- Iatrogenic causes, or bleeding due to medical treatment or intervention, such as sex steroids, anticoagulants, or intrauterine contraceptive devices

- Infection

Placenta accreta occurs when all or part of the placenta attaches abnormally to the myometrium (the muscular layer of the uterine wall). Three grades of abnormal placental attachment are defined according to the depth of attachment and invasion into the muscular layers of the uterus:

- Accreta – chorionic villi attach to the myometrium, rather than being restricted within the decidua basalis.

- Increta – chorionic villi invade into the myometrium.

- Percreta – chorionic villi invade through the perimetrium (uterine serosa).

Because of abnormal attachment to the myometrium, placenta accreta is associated with an increased risk of heavy bleeding at the time of attempted vaginal delivery. The need for transfusion of blood products is frequent, and hysterectomy is sometimes required to control life-threatening hemorrhage.

Clinically, Breus' mole may be asymptomatic, or may present with signs of decreased blood flow to the foetus such as growth restriction and foetal distress. Postnatally, Breus' mole is found in placental examination following live birth or spontaneous abortion. Breus' mole is diagnosed antinatally by ultrasound, where a thick multilobulated hematoma can be seen beneath the chorion. Occasionally, subchorial thrombohematoma may later become intraplacental, making its diagnosis difficult. The mole may be echogenic or hypoechoic depending upon the amount of fresh blood present in it. Breus' mole should be differentiated from vesicular mole and missed abortion in an ultrasound examination.

Symptoms may include visible discoloring (ecchymosis), breast pain, and swelling.

The symptoms may be similar to those of fibrocystic breast changes.

Breus' mole (Ova tuberculosa, massive mole) is a massive, subchorionic, tuberous hematoma, formed out of maternal blood in the uterus in pregnancy. It was first described by Karl Breus in 1892.

When the antepartum diagnosis of placenta accreta is made, it is usually based on ultrasound findings in the second or third trimester. Sonographic findings that may be suggestive of placenta accreta include:

1. Loss of normal hypoechoic retroplacental zone

2. Multiple vascular lacunae (irregular vascular spaces) within placenta, giving "Swiss cheese" appearance

3. Blood vessels or placental tissue bridging uterine-placental margin, myometrial-bladder interface, or crossing the uterine serosa

4. Retroplacental myometrial thickness of <1 mm

5. Numerous coherent vessels visualized with 3-dimensional power Doppler in basal view

Although there are isolated case reports of placenta accreta being diagnosed in the first trimester or at the time of abortion <20 weeks' gestational age, the predictive value of first-trimester ultrasound for this diagnosis remains unknown. Women with a placenta previa or "low-lying placenta" overlying a uterine scar early in pregnancy should undergo follow-up imaging in the third trimester with attention to the potential presence of placenta accreta.

Both are composed of intermediate trophoblast, but their morphological features and clinical presentation can differ significantly.

Exaggerated placental site is a benign, non cancerous lesion with an increased number of implantation site intermediate trophoblastic cells that infiltrate the endometrium and the underlying myometrium. An exaggerated placental site may occur with normal pregnancy, or after an abortion. No specific treatment or follow up is necessary.

Placental site nodules are lesions of chorionic type intermediate trophoblast, usually small. 40 to 50% of placental site nodules are found in the cervix. They almost always are incidental findings after a surgical procedure. No specific treatment or follow up is necessary.

Gestational trophoblastic disease (GTD) is a term used for a group of pregnancy-related tumours. These tumours are rare, and they appear when cells in the womb start to proliferate uncontrollably. The cells that form gestational trophoblastic tumours are called trophoblasts and come from tissue that grows to form the placenta during pregnancy.

There are several different types of GTD. Hydatidiform moles are benign in most cases, but sometimes may develop into invasive moles, or, in rare cases, into choriocarcinoma, which is likely to spread quickly, but which is very sensitive to chemotherapy, and has a very good prognosis. Gestational trophoblasts are of particular interest to cell biologists because, like cancer, these cells invade tissue (the uterus), but unlike cancer, they sometimes "know" when to stop.

GTD can simulate pregnancy, because the uterus may contain fetal tissue, albeit abnormal. This tissue may grow at the same rate as a normal pregnancy, and produces chorionic gonadotropin, a hormone which is measured to monitor fetal well-being.

While GTD overwhelmingly affects women of child-bearing age, it may rarely occur in postmenopausal women.

Breast hematoma is a collection of blood within the breast. It arises from internal bleeding (hemorrhage) and may arise due to trauma (breast injury or surgery) or due to a non-traumatic cause.

Molar pregnancies usually present with painless vaginal bleeding in the fourth to fifth month of pregnancy. The uterus may be larger than expected, or the ovaries may be enlarged. There may also be more vomiting than would be expected (hyperemesis). Sometimes there is an increase in blood pressure along with protein in the urine. Blood tests will show very high levels of human chorionic gonadotropin (hCG).

A lymphocele is a collection of lymphatic fluid within the body not bordered by epithelial lining. It is usually a surgical complication seen after extensive pelvic surgery (such as cancer surgery) and is most commonly found in the retroperitoneal space. Spontaneous development is rare.

Many lymphoceles are asymptomatic. Larger lymphoceles may cause symptoms related to compression of adjacent structures leading to lower abdominal pain, abdominal fullness, constipation, urinary frequency, and edema of the genitals and/or legs. Serious sequelae could develop and include infection of the lymphocele, obstruction and infection of the urinary tract, intestinal obstruction, venous thrombosis, pulmonary embolism, chylous ascites and lymphatic fistula formation.

On clinical examination the skin may be reddened and swollen and a mass felt. Ultrasonography or CT scan will help to establish a diagnosis.

Other fluid collections to be considered in the differential diagnosis are urinoma, seroma, hematoma, as well as collections of pus. Also, when lower limb edema is present, venous thrombosis needs to be considered.

Molar pregnancy is an abnormal form of pregnancy in which a non-viable fertilized egg implants in the uterus and will fail to come to term.

A molar pregnancy is a gestational trophoblastic disease which grows into a mass in the uterus that has swollen chorionic villi. These villi grow in clusters that resemble grapes. A molar pregnancy can develop when a fertilized egg does not contain an original maternal nucleus. The products of conception may or may not contain fetal tissue. It is characterized by the presence of a hydatidiform mole (or hydatid mole, mola hydatidosa). Molar pregnancies are categorized as partial moles or complete moles, with the word "mole" being used to denote simply a clump of growing tissue, or a "growth".

A complete mole is caused by a single sperm (incidence is about 90%) or two (incidence is about 10%) sperms combining with an egg which has lost its DNA (in the first case the sperm then reduplicates forming a "complete" 46 chromosome set). The genotype is typically 46,XX (diploid) due to subsequent mitosis of the fertilizing sperm, but can also be 46,XY (diploid). 46,YY (diploid) is not observed. In contrast, a partial mole occurs when a haploid egg is fertilized by two sperm or by one sperm which reduplicates itself yielding the genotypes of 69,XXY (triploid) or 92,XXXY (tetraploid). Complete hydatidiform moles have 2 - 4% risk of developing into choriocarcinoma in Western countries and 10 - 15% in Eastern countries and overall, also a 15% chance of becoming an invasive mole. Incomplete moles can become invasive (<5% risk) but are not associated with choriocarcinoma. Complete hydatidiform moles account for 50% of all cases of choriocarcinoma.

It is diagnosed by a microscopic examination of the placenta.

Commonly used criteria from Altshuler are: "a minimum of 10 villi, each with 10 or more vascular channels, in 10 or more areas of 3 or more random, non-infarcted placental areas when using a ×10 ocular." The Altshuler criteria are not theoretically rigorous, as they do not define the area. Normal villi have up to five vascular channels.

The symptoms of a perianal hematoma can present over a short period of time. Pain, varying from mild to severe, will occur as the skin surrounding the rupture expands due to pressure. This pain will usually last even after the blood has clotted, and may continue for two to four days.

Theca lutein cyst is a type of bilateral functional ovarian cyst filled with clear, straw-colored fluid. To be classified a functional cyst, the mass must reach a diameter of at least three centimeters.

These cysts result from exaggerated physiological stimulation (hyperreactio luteinalis) and are usually associated with markedly elevated levels of beta-human chorionic gonadotropin (beta-hCG). They are thus associated with gestational trophoblastic disease (molar pregnancy), diabetes mellitus, alloimmunisation to Rh-D, and multiple gestations. They have rarely been associated with chronic kidney disease (secondary to reduced hCG clearance) and hyperthyroidism (given the structural homology with TSH). These cysts resolve after pregnancy. Rarely, when the theca-lutein cysts are stimulated by gonadotropins, massive ascites can result. In most cases however, abdominal symptoms are minimal and restricted to peritoneal irritation from cyst hemorrhage. Surgical intervention may be required to remove ruptured or infarcted tissue.

Women who smoke have a twofold increase for functional cysts.

Chorangiosis is a placental pathology characterized by an abundance of blood vessels within the chorionic villi.

Perianal hematoma is a hematoma located in, or on the border of the anus. It is sometimes inappropriately referred to as an external hemorrhoid.

Placental site trophoblastic tumor is a form of gestational trophoblastic disease, which is thought to arise from intermediate trophoblast.

It may secrete human placental lactogen (human chorionic somatomammotropin), and result in a false-positive pregnancy test.

Placental site trophoblastic tumor is a monophasic neoplasm of the implantation site intermediate trophoblast, and usually a benign lesion, which comprises less than 2% of all gestational trophoblastic proliferations. Preceding conditions include molar pregnancy (5%). Compared to choriocarcinoma or invasive mole, hemorrhage is less conspicuous and serum β-HCG level is low, making early diagnosis difficult.

Immunohistochemistry: Often stains with hPL, keratin, Mel-CAM, EGFR.

Prognosis: 10–20% of cases metastase leading to death.

Treatment: Because chemotherapy is ineffective; the patient should undergo hysterectomy.

Chorioamnionitis also known as intra-amniotic infection (IAI) is an inflammation of the fetal membranes (amnion and chorion) due to a bacterial infection. It typically results from bacteria ascending into the uterus from the vagina and is most often associated with prolonged labor. The risk of developing chorioamnionitis increases with each vaginal examination that is performed in the final month of pregnancy, including during labor.

Chorioamnionitis is diagnosed clinically in the setting of Maternal fever (≥ 100.4 °F) and at least two of the following:

- Maternal leukocytosis (> 15,000 cells/mm³)

- Maternal tachycardia (> 100 bpm)

- Fetal tachycardia (> 160 bpm)

- Uterine tenderness

- Foul odor of amniotic fluid

Exclusions:

- Maternal upper respiratory infection.

- Maternal urinary tract infection.

The diagnosis is generally a clinical one, with a fluctuant boggy mass developing over the scalp (especially over the occiput) with superficial skin bruising. The swelling develops gradually 12–72 hours after delivery, although it may be noted immediately after delivery in severe cases. The hematoma spreads across the whole calvaria as its growth is insidious and may not be recognized for hours. If enough blood accumulates a visible fluid wave may be seen. Patients can develop raccoon eyes.

Patients with subgaleal hematoma may present with hemorrhagic shock. The swelling may obscure the fontanel and cross suture lines (distinguishing it from cephalohematoma). Watch for significant hyperbilirubinemia. The long-term prognosis is generally good. Laboratory studies consist of a hematocrit evaluation.