When a child's sex is not clear at birth, the child has atypical genitalia (ambiguous genitalia). This means that the genitals don't seem to be clearly male or female. You may hear these differences called "DSDs," or sometimes "disorders of sexual development."

Atypical genitalia can be a difficult experience for families.

You have 46 chromosomes in each cell of your body. These are grouped into 23 pairs. The 23rd pair determines your sex. Females have two X chromosomes, and males have one X and one Y chromosome.

The sex of a developing baby is determined at conception, when the embryo has either two XX chromosomes, or an X and a Y chromosome. Around the 6th week of the unborn baby's development, a gene on the Y chromosome of a developing male tells the fetal tissue that will form the sex organs to become the testes.

As the testes make testosterone, the penis, scrotum, and urethra form. Then during the 7th to 8th month of the pregnancy, the testes descend into the scrotum.

Without the Y chromosome, the fetal tissue in a female baby that will form the sex organs becomes the ovaries, uterus, and fallopian tubes.

Certain hormones also can affect the development of the sex organs. These hormones are secreted during the early weeks of gestation.

Many genetic and environmental factors can affect the developing baby and lead to atypical genitalia. Ambiguous genitalia may make it harder to determine a baby's sex. But very few newborns with this condition have genitals that are so ambiguous that the doctor can't figure out the sex at birth.

The far more common cases at birth are:

• A female baby who seems to have a small penis because the baby has a high level of male hormones (virilization).
• A male baby with an abnormally small penis that looks like a female clitoris. This is either because the baby did not respond to male hormones or the baby did not make male hormones.

Atypical genitalia can have a number of different causes. In many cases, doctors don't know the cause. It seems to occur by chance.

Children who are born with atypical genitalia may fall into one of these groups.

These children have:

• Tissue that is related to both the ovaries and the testes.
• Both male and female internal sex organs.
• External genitalia that are partly ambiguous.
• Chromosomes that are either normal female or male, or a mixture (mosaic).

These children have:

• An undeveloped sex organ.
• Internal sex organs that are often female.
• External genitals that may vary between normal female and normal male. Most are female.
• Chromosomes that are normal, have only an X chromosome, or are a mixture (mosaic).

This affects female babies. Those with this condition have male chromosomes, underdeveloped sex organs, internal female reproductive organs, and female external genitalia.

Children with this condition have questionable external genitalia. But they have only one sex's internal sex organs.

46,XX DSDmeans that the child has female internal sex organs.

46,XY DSD means that the child has male internal sex organs. The two primary causes of 46,XY DSD are androgen insensitivity syndrome and 5-alpha reductase deficiency.

These children have:

• Normal male chromosomes.
• Normal female external genitalia.

This is called androgen insensitivity syndrome because these male babies don't respond to testosterone (androgens). This syndrome is inherited. It's caused by a problem with a gene on the X chromosome. This problem is called X-linked recessive. Females who carry the gene have a 1 in 2 chance of having a male child with the syndrome. Female children born to females who carry the gene have a 1 in 2 chance of being carriers of the gene.

Children with this condition have:

• Normal male chromosomes.
• Genitals that are ambiguous.

Children with this condition lack an enzyme (5-alpha reductase). This enzyme is needed to help the male sex organs complete their development. This condition is inherited. It's caused by an autosomal recessive gene. Autosomal recessive means that each parent carries one copy of the gene and transmits the gene at the same time to the child. Carrier parents have a 1 in 4 chance of having a child with this condition with each pregnancy. It affects only male babies.

46,XX DSD has a number of causes.

Female babies with this condition have male sex organs. The condition is caused by a lack of a certain enzyme in the adrenal gland. It's the most common cause of atypical genitalia in newborns.

The condition is inherited and passed on by an autosomal recessive gene. Autosomal recessive means that each parent carries one copy of the gene and passes on the gene to the child. Carrier parents have a 1 in 4 chance of having a child with this condition with each pregnancy. Female babies with the condition have atypical genitalia. Male babies don't.

In some cases, the female parent of a child with this condition can be given medicines during pregnancy to reduce the effects of the enzyme deficiency if the baby is female.

Another type of CAH is called salt-losing. This is very serious and often fatal. It causes an electrolyte collapse in the newborn. Treatment is available if diagnosed early. Males and females are equally affected.

Other, rarer enzyme problems can also cause CAH in either male babies or female babies.

This condition is often caused by a problem with the adrenal glands. High levels of male hormones may also enter the placenta via the pregnant parent. This could happen when progesterone is given to prevent a miscarriage. Or it can happen if the pregnant parent has a hormone-producing tumor.

When a child's genitalia are ambiguous at birth, the child's doctor will ask about your health history. The health history will include your health during pregnancy and a family history of any neonatal deaths or genital abnormalities. The doctor will also do a physical exam of your child's external genitalia.

Your child's doctor will look for the underlying cause of the disorder. Your child may need a newborn screening test for CAH, hormone studies, and a biopsy of the sex organs.

To figure out the sex, your child's doctor will look at the following:

• A pelvic ultrasound to check for the female sex organs. Or the doctor may use direct cystoscopy or vaginoscopy.
• A genitourethrogram to look at the urethra and vagina, if present.
• A chromosome study to help figure out the genetic sex of the child.
• Evaluation of the gene on the Y chromosome that starts development of the male sex organs.
• How fertile a child may be who has 46,XX DSD.
• Size and possibility for growth of a penis present in a child who has 46,XY DSD.
• Ability of an internal sex organ to make the appropriate sex hormones for the sex assigned to the child.
• Risk of future health conditions (such as cancer) that may develop in the original sex organs later in life.
• The actions of male or female hormones on the fetal brain.
• Your opinion or preference.

Sometimes a child with atypical genitalia is at higher risk for tumors in the sex organs. Treatment for atypical genitalia depends on the type of the disorder. But it often includes surgery to remove or create sex organs appropriate for the child's sex. Treatment may also include hormone therapy.

Most important, you and your family should be included early in the decision of assigning the child's sex. Ask your doctor about what is available for long-term psychological support.

Making a correct determination of sex is important for treatment. But it's also important for the child's emotional well-being. Some children born with atypical genitalia may have normal internal sex organs that allow them to live normal, fertile lives. But others may have problems with fertility as adults.