Early in fetal development, the tissue that will become the gonads (ovaries or testes) is identical and has the potential to become either ovaries or testes, depending on the genetics of the fetus. Humans have 46 chromosomes in each cell of their body, or 23 pairs. The 23rd pair is important for sex determination; females usually have two X chromosomes, while males usually have one X and one Y chromosome.
There is a gene located on the short arm (top half) of the Y chromosome, called SRY, which, if present, will cause the gonad to become testes (indicating a male) around the sixth week of fetal life. At the same time, the tissue that would have become the female reproductive organs (uterus and fallopian tubes) will disappear. As the testes produce testosterone (male hormone), the phallus (penis), scrotum and urethra form. Later, during the seventh to eighth month of the pregnancy, the testes will descend into the scrotum.
In the absence of the SRY gene, the gonad will become an ovary (indicating a female). Likewise, the female reproductive tract will continue to develop, forming the uterus and fallopian tubes. At the same time, the tissue that would have become the male reproductive organs (epididymis and vas deferens) occurs.
Changes in a number of genetic or hormonal factors can affect this process, leading to ambiguous genitalia. Ambiguous genitalia, as the word implies, may make determining the child's gender more difficult. More recently, the term Differences (or Disorders) of Sex Development (DSD) has been used to describe conditions in which the child’s genetics, hormones, internal organs or external genitalia are atypical.
It is important to know:
- These conditions are not as rare as most think and affect about 1 in 100 newborns.
- There is a wide variety of conditions which can cause ambiguous genitalia and sometimes a detailed evaluation needs to take place before the sex of the child is clear.
- Children with DSD can sometimes have other congenital problems, but in general these children are healthy.
- One of the more common conditions known as congenital adrenal hyperplasia needs to be diagnosed and treated soon after birth to avoid serious illness in the baby.