Birth defects occur for a number of reasons, though they are most often influenced in the first trimester of pregnancy. The Centers for Disease Control and Prevention (CDC) in the United States estimates that every one in 33 babies is born with some form of birth defect, ranging from mild and asymptomatic to life-threatening, and they can be either preventable (i.e. influenced by the mother and her environment) or heritable (i.e. genetic). Major birth defects cause structural changes in a part of the anatomy, having adverse effects on health and, often, long-term quality of life due to increased risk of illness and disability. Birth defects can affect both sexes, though each has particular susceptibilities due to anatomical differences.
Female genital birth defects
The differences between birth defects in males and females are most discernible in regards to genital defects. Female is defined genetically based on the presence of two X chromosomes (genotype 46XX, as opposed to male, 46XY), but the presence of female reproductive tissue (and lack of male reproductive tissue) is also considered an indicator of gender. Abnormal levels of male sex hormones during fetal development, due to congenital adrenal hyperplasia, maternal treatment with progesterone or a maternal hormone-producing tumor, can lead to alterations in the external female genitalia.
Ambiguous external genitalia, also known as an intersex state, in the form of an enlarged clitoris can confuse determining the sex of the baby without genetic testing or examination for the presence of ovaries. The condition is referred to as pseudohemaphroditism or virilization. The physical condition is often corrected by surgery after genetic confirmation of sex. The surgical correction also corrects any malformation of the vagina and urethra, as urinary tract defects often accompany genital defects due to the overlap of the reproductive and excretion systems.
Defects of the vagina and uterus are called Mullerian anomalies, named for embryonic development from the Mullerian duct. The defects are usually not detected until puberty, when young girls experience pelvic pain, irregular menstruation or other reproductive issues, because the ovaries and external genitalia are normal. The most common defects are agenesis and hypoplasia, in which the tract or part of the tract (such as the vagina) does not form. There are also several uterine defects.
- Unicornuate uterus: only half the uterus forms (banana-shaped). The condition is rare and often accompanied by kidney agenesis.
- Uterus didelphys: double uterus, potentially including duplication of the vagina and cervix.
- Bicornuate uterus: misshaped womb with two horns (heart shaped instead of pear shaped, impinging on the baby's room to grow).
- Septate uterus: a wall of tissue divides the uterus.
- Diethylstilbestrol (DES)-related uterus: T-shaped uterus in the child due to maternal exposure to the drug, also increases risk of vaginal cancer in the child.
- Arcuate uterus: slight variation in the shape of the uterus, considered simply as a variation of the norm.
Whether fertility is affected depends on the exact type and extent of defect. Some can be surgically remedied to alleviate painful menstruation.
Other female reproductive tract defects
Other potential defects of the female reproductive tract include cloacal abnormalities. The cloaca is the initial tube from which the rectum, urinary tract and vagina form - persistence late into development can result in a lack of the appropriate orifices, resulting in severe pain and gastrointestinal disruption, as well as the appearance of male genitalia.
Also, the vaginal opening may be completely blocked, called imperforate hymen. This condition is usually discovered when menstruation begins.
An extra ovary or extra tissue on the ovaries may be present as a birth defect, as well as ovotestes, the presence of both male and female tissue.
When a baby is born with only one sex chromosome it is known as monosomy. In females it is X monosomy (45X genotype), which is referred to as Turner syndrome, or gonadal dysgenesis, and occurs in an estimated one of every 2500 live female births according to the National Institutes of Health.
Sometimes the second X chromosome is only partially missing. Children born with this condition have swollen hands and feet, and sometimes a wide webbed neck. As the child matures they lack secondary sex characteristics (i.e. no puberty) unless treated with estrogen. Children may also have a short stature unless treated with growth hormone. Menstruation is absent and an adult with Turner’s is infertile. The condition has a number of complications, including heart defects, autoimmune disorders (e.g. Hashimoto’s thyroiditis and diabetes), arthritis and cataracts.
Because gender-specific birth defects tend to affect the reproductive organs, they may not be noticed or affect the individual until puberty. Female babies can be affected by Mullerian anomalies, X chromosome abnormalities such as monosomy, and even problems with reproductive tract development. Many of the defects can be treated surgically or hormonally, but the effects on fertility depend on the exact medical issue.