The purpose of prenatal diagnostic testing is to determine whether a fetus has certain abnormalities before birth (prenatally), including certain genetic disorders that are hereditary or spontaneous.
- Ultrasonography and measurement of certain substances in a pregnant woman’s blood can help estimate the risk of genetic abnormalities in the fetus.
- During pregnancy, blood tests and ultrasonography may be performed as part of routine care.
- In the event that the results of these tests indicate an increased risk, doctors may perform tests to analyze the genetic material of the fetus. This includes amniocentesis and chorionic villus sampling.
- It is critical to note that amniocentesis and chorionic villus sampling are invasive procedures with very low risks to the fetus.
Prenatal diagnostic tests, such as ultrasounds and certain blood tests, are often included in routine prenatal care. Ultrasonography and blood tests are safe and may be used to determine whether more invasive prenatal genetic tests are required (chorionic villus sampling, amniocentesis, and percutaneous umbilical blood sampling). Most commonly, these more invasive tests are performed when couples are at an increased risk of having a child with a genetic abnormality (such as a neural tube defect) or a chromosomal abnormality (particularly if the woman is 35 or older). Many doctors offer this type of testing to all pregnant women, and it can be requested by any pregnant woman. These tests have risks, even though they are small, especially for the fetus.
Couples should discuss the risks with their health care practitioner and weigh them against their need to be informed. Consider, for example, whether not knowing the results of testing would cause anxiety, and whether knowing that an abnormality was not detected would be reassuring. If an abnormality is discovered, they should decide whether they would seek an abortion. In this case, they should consider whether they still wish to know about an abnormality before birth (to prepare psychologically) or whether knowing would only be distressing. There are some couples who decide not to get tested for chromosomal abnormalities because the risks outweigh the benefits.
Genetic disorders can sometimes be diagnosed before the fertilized egg is transferred from the culture dish to the uterus (called preimplantation genetic diagnosis).