Most prenatal development occurs normally, following the established patterns with little variation. However, there are a number of things that can go wrong during this time, which are usually caused by genetics or environmental problems.
Clearly, genetics play a major role in development. However, in some cases genetic problems can emerge that may impact both current and future development.
- Down Syndrome - Also known as trisomy 21, Down syndrome is the most common genetic anomaly during prenatal development. Down syndrome is caused by and extra copy of the 21 chromosome (meaning there are three chromosomes instead of the usual two) and impacts approximately 1 out of every 1,000 infants. Typical features of Down syndrome include flattened facial features, heart defects, and mental retardation. The risk of having a child with Down syndrome increases with maternal age.
- Inherited diseases - A number of illnesses can be inherited if one or both parents carries a gene for the disease. Examples of inherited diseases include Sickle-cell anemia, Cystic fibrosis, and Tay-Sachs disease. Genetic tests can often determine if a parent is a carrier of genes for a specific disease.
- Sex-Chromosome Problems - A third type of genetic problems involves sex-chromosomes. These includes conditions such as Klinefelter's syndrome (an extra X-chromsome) and Turner syndrome (a single X-chromosome).
Environmental variables can also play a major role in prenatal development. Harmful environmental elements that can effects the fetus are known as teratogens. There a number of teratogens that can harm the fetus, including:
- Maternal Drug Use - The use of substances by the mother can have devastating consequences to the fetus. Smoking is linked to low birth weight, which can result in a weakened immune system, poor respiration, and neurological impairment. Alcohol use can lead to fetal alcohol syndrome, which is linked to heart defects, body malformations, and mental retardation. The use of illicit psychoactive drugs such as cocaine and methamphetamine is also linked to low birth weight and neurological impairment.
- Maternal Disease - There are a number of maternal diseases that can negatively impact the fetus, including herpes, rubella, and AIDS. Herpes virus is one of the most common maternal diseases and can be transmitted in the fetus, leading to deafness, brain swelling, or mental retardation. Women with herpes virus are often encouraged to deliver via cesarean to avoid transmission of the virus.