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).

Invasive hydatidiform mole, also known as invasive mole and chorioadenoma destruens is a type of neoplasia that grows into the muscular wall of the uterus. It is formed after conception (fertilization of an egg by a sperm). It may spread to other parts of the body, such as the vagina, vulva, and lung.

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.

A placental disease is any disease, disorder, or pathology of the placenta. The article also covers placentation abnormalities, which is often used synonymously for placental disease.

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.

Trophoblastic neoplasms derive from trophoblastic tissue. Examples include:

- Choriocarcinoma

- Hydatidiform mole

Gestational trophoblastic disease (GTD) may also be called gestational trophoblastic tumour (GTT).

Hydatidiform mole (one type of GTD) may also be called molar pregnancy.

Persistent disease; persistent GTD: If there is any evidence of persistence of GTD, usually defined as persistent elevation of beta hCG (see «Diagnosis» below), the condition may also be referred to as gestational trophoblastic neoplasia (GTN).

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.

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.

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.

Signs of duct ectasia can include nipple retraction, inversion, pain, and sometimes bloody discharge.

According to the American Academy of Dermatology, the most common types of moles are skin tags, raised moles and flat moles. Benign moles are usually brown, tan, pink or black (especially on dark-colored skin). They are circular or oval and are usually small (commonly between 1–3 mm), though some can be larger than the size of a typical pencil eraser (>5 mm). Some moles produce dark, coarse hair. Common mole hair removal procedures include plucking, cosmetic waxing, electrolysis, threading and cauterization.

Some sources equate the term mole with "melanocytic nevus". Other sources reserve the term "mole" for other purposes such as the animal of the same name.

Melanocytic nevi represent a family of lesions. The most common variants are:

- Location:

- Junctional nevus: the nevus cells are located along the junction of the epidermis and the underlying dermis. A junctional nevus is flat and brown to black.

- Compound nevus: a mixture of junctional and intradermal proliferation. Compound nevi are slightly raised and brown to black. Beauty marks are usually compound nevi of either the acquired variety or congenital variety.

- Intradermal nevus: the nevus cells are located in the dermis only. Intradermal nevi are raised; most are flesh-colored (not pigmented).

- Dysplastic nevus (nevus of Clark): usually a compound nevus with cellular and architectural dysplasia. Like typical moles, dysplastic nevi can be flat or raised. While they vary in size, dysplastic nevi are typically larger than normal moles and tend to have irregular borders and irregular coloration. Hence, they resemble melanoma, appear worrisome, and are often removed to clarify the diagnosis. Dysplastic nevi are markers of risk when they are numerous (atypical mole syndrome). According to the National Cancer Institute (NIH), doctors believe that, when part of a series or syndrome of multiple moles, dysplastic nevi are more likely than ordinary moles to develop into the most virulent type of skin cancer called melanoma.

- Blue nevus: It is blue in color as its melanocytes are very deep in the skin. The nevus cells are spindle shaped and scattered in deep layers of the dermis. The covering epidermis is normal.

- Spitz nevus: a distinct variant of intradermal nevus, usually in a child. They are raised and reddish (non-pigmented). A pigmented variant, called the 'nevus of Reed', typically appears on the leg of young women.

- Acquired nevus: Any melanocytic nevus that is not a congenital nevus or not present at birth or near birth. This includes junctional, compound and intradermal nevus.

- Congenital nevus: Small to large nevus present at or near time of birth. Small ones have low potential for forming melanomas, however the risk increases with size, as in the giant pigmented nevus.

- Giant pigmented nevus: these large, pigmented, often hairy congenital nevi. They are important because melanoma may occasionally (10 to 15%) appear in them.

- Intramucosal nevus: junctional nevus of the mucosa of the mouth or genital areas. In the mouth, they are found most frequently on the hard palate.

- Nevus of Ito and nevus of Ota: congenital, flat brownish lesions on the face or shoulder.

- Mongolian spot: congenital large, deep, bluish discoloration which generally disappears by puberty. It is named for its association with East Asian ethnic groups but is not limited to them.

- Recurrent nevus: Any incompletely removed nevus with residual melanocytes left in the surgical wound. It creates a dilemma for the patient and physician, as these scars cannot be distinguished from a melanoma.

Port-wine stains, also known as nevus flammeus and sometimes mistaken for strawberry marks, are present at birth and range from a pale pink in color, to a deep wine-red. Irregular in appearance, they are usually quite large, and caused by a deficiency or absence in the nerve supply to blood vessels. This causes vasodilation, the dilation of blood vessels, causing blood to pool or collect in the affected area. Over time, port-wine stains may become thick or develop small ridges or bumps, and do not fade with age. Such birthmarks may have emotional or social repercussions. Port-wine stains occur in 0.3% of the population, equally among males and females. They frequently express unilaterally, i.e., on only one side, not crossing the midline of the body. Often on the face, marks on the upper eyelid or forehead may be indicative of a condition called Sturge-Weber syndrome. Additionally, port-wine stains in these locations may be associated with glaucoma and seizures.

Halo nevi are also known as Sutton's nevi, or leukoderma acquisitum centrifugum. Halo nevi are named such because they are a mole (nevi) that is surrounded by an area of depigmentation that resembles a halo.

Halo nevi are associated with vitiligo. Sometimes the pale (hypopigmented) areas will spontaneous regress, and pigment returns.

Noninvasive methods to determine duct diameter in live patients are available only recently and it is not clear how the results should be compared with older results from biopsies.

Histologically, dilation of the large duct is prominent. Duct widening with associated periductal fibrosis is frequently included in the wastebasket definition of fibrocystic disease.

In plasma cell rich lesions diagnosed on core biopsies, steroid-responsive IgG4-related mastitis can be identified by IgG/IgG4 immunostaining.

A "hemangioma of infancy", colloquially called a strawberry mark, is a benign self-involuting tumor (swelling or growth) of endothelial cells, the cells that line blood vessels. It usually appears during the first weeks of life and resolves by age 10. It is the most common tumor of infancy.

PHACES Syndrome, a rare condition that often involves brain, heart, and arterial abnormalities, is generally accompanied by the presence of large facial hemangiomas. In such cases, what appears to be a small bruise or birthmark may grow rapidly and take on a puffy appearance in the first days or weeks of life.

Halo nevus (also known as "Leukoderma acquisitum centrifugum," "Perinevoid vitiligo," and "Sutton nevus") is a mole that is surrounded by a depigmented ring or 'halo'.

The congenital melanocytic nevus appears as a circumscribed, light brown to black patch or plaque, potentially very heterogeneous in consistency, covering any size surface area and any part of the body.

As compared with a melanocytic nevus, congenital melanocytic nevi are usually larger in diameter and may have excess terminal hair, a condition called hypertrichosis. If over 40 cm projected adult diameter with hypertrichosis, it is sometimes called giant hairy nevus; more usually these largest forms are known as large or giant congenital melanocytic nevus. The estimated prevalence for the largest forms is 0.002% of births.

Melanocytic Nevi often grow proportionally to the body size as the child matures. As they mature, they often develop thickness, and become elevated, although these features can also be present from birth. Prominent terminal hairs often form, especially after puberty. With maturity, the nevus can have variation in color, and the surface might be textured with proliferative growths.

Neurocutaneous melanosis is associated with the presence of either giant congenital melanocytic nevi or non-giant nevi of the skin. It is estimated that neurocutaneous melanosis is present in 2% to 45% of patients with giant congenital melanocytic nevi. Neurocutaneous melanosis is characterized by the presence of congenital melanocytic nevi on the skin and melanocytic tumors in the leptomeninges of the central nervous system.

Trophoblastic neoplasms are neoplasms which derive from trophoblastic tissue.

Examples include:

- choriocarcinoma

- hydatidiform mole

Congenital melanocytic nevi may be divided into the following types:

- "Small-sized congenital melanocytic nevus" is defined as having a diameter less than 2 cm.

- "Medium-sized congenital melanocytic nevus" is defined as having a diameter more than 2 cm but less than 20 cm.

- "Giant congenital melanocytic nevus" (also known as "Bathing trunk nevus," "Garment nevus," "Giant hairy nevus", and "Nevus pigmentosus et pilosus") is defined by one or more large, darkly pigmented and sometimes hairy patches.

It is characterized by a nearly symmetrical presence of a spoon hand (classical type) or, more frequently, an oligodactylous hand. Individuals with this syndrome present the following symptoms: carpal, metacarpal and digital synostoses, disorganization of carpal bones, numeric reduction of digital rays and toe syndactyly. Additionally, other symptoms may include radioulnar synostosis, brachymesomelia, radius head dislocation, metatarsal synostoses and numeric reduction of rays.

A junctional nevus is a mole found in the junction (border) between the epidermis and dermis layers of the skin.

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

Additional types of nevi do not involve disorders of pigmentation or melanocytes. These additional nevi represent hamartomatous proliferations of the epithelium, connective tissue, and vascular malformations.