Ambiguous genitalia is a birth defect where the outer genitals do not have the typical appearance of either a boy or a girl.

See also: Genetics

The genetic sex of a child is determined at conception. The mother's egg cell (ovum) contains an X chromosome, while the father's sperm cell contains either an X or a Y chromosome. These X and Y chromosomes determine the child's genetic sex.

Normally, an infant inherits one pair of sex chromosomes -- one X from the mother and one X or one Y from the father. Thus, it is the father who "determines" the genetic sex of the child. A baby who inherits the X chromosome from the father is a genetic female (two X chromosomes). A baby who inherits the Y chromosome from the father is a genetic male (one X and one Y chromosome). The male and female reproductive organs and genitals both arise from the same tissue in the fetus.

If the process that causes this fetal tissue to become "male" or "female" is disrupted, ambiguous genitalia can develop. This genitalia makes it difficult to classify the infant as male or female. The extent of the ambiguity varies. In very rare instances, the physical appearance may be fully developed as the opposite of the genetic sex. For example,  a genetic male may have developed the appearance of a normal female.

Typically, ambiguous genitalia in genetic females (babies with two X chromosomes) has the following features:

• An enlarged clitoris that has the appearance of a small penis.
• The urethral opening (where urine comes out) can be anywhere along, above, or below the surface of the clitoris.
• The labia may be fused, resembling a scrotum.
• The infant may be thought to be a male with undescended testicles.
• Sometimes a lump of tissue is felt within the fused labia, further making it look like a scrotum with testicles.

In a genetic male (one X and one Y chromosome), ambiguous genitalia typically include the following features:

• A small penis (less than 2-3 centimeters or 0.8-1.2 inches) that resemble an enlarged clitoris (the clitoris of a newborn female is normally somewhat enlarged at birth).
• The urethral opening may be anywhere along, above, or below the penis; it can be placed as low as on the peritoneum, further making the infant appear to be female.
• There may be a small scrotum with any degree of separation, resembling labia.
• Undescended testicles commonly accompany ambiguous genitalia.

Ambiguous genitalia is usually not life threatening (see Causes section for exceptions ), but can create social  problems for the child and the family. For this reason, a team of experienced specialists, including neonatologists, geneticists, endocrinologists, and psychiatrists or social workers will be involved.

• Pseudohermaphroditism. The genitalia are of one sex, but some physical characteristics of the other sex are present.
• True hermaphrodism. A very rare condition in which both ovarian and testicular tissue is present. The child may have parts of both male and female genitalia.
• Mixed gonadal dysgenesis (MGD). An intersex condition in which there appears some male structures (gonad, testis), as well as a uterus, vagina, and fallopian tubes.
• Congenital adrenal hyperplasia. This condition has several forms, but the most common form causes the genetic female to appear male. Many states test for this potentially life-threatening condition during newborn screening exams.
• Chromosomal abnormalities, includingKlinefelter's syndrome (XXY) andTurner's syndrome (XO).
• Maternal ingestion of certain medications (particularly androgenic steroids) may make a genetic female look more male
• Lack of production of specific hormones can cause the embryo to develop with a female body type regardless of genetic sex
• Lack of testosterone cellular receptors. So even if the body makes the hormones needed to develop into a physical male, the body is unable to respond to those hormones, and therefore, a female body-type is the result even if the genetic sex is male.