What is a Prenatal Genetic Screening?

Prenatal genetic screening involves medical testing on the unborn baby to check for certain chromosomal abnormalities, such as Down syndrome. There are various types of testing when performing a prenatal genetic screening, including blood tests and amniotic fluid testing. These tests are all voluntary, and the patient should discuss all risks and concerns with her doctor.

Each pregnancy is divided roughly into three-month segments, known as trimesters. Prenatal genetic screening tests vary according to trimester. For example, during the first trimester of pregnancy, blood tests and ultrasounds may be used to check for conditions such as Down syndrome and trisomy 18. Down syndrome is caused by the presence of an extra chromosome known as chromosome 21 and often causes physical and mental challenges in the patient born with this condition. Trisomy 18 causes an extra chromosome known as the 18th chromosome, leading to impaired physical, developmental, and mental functioning.

If the blood tests performed during the first trimester indicate a higher than normal risk for chromosomal abnormalities, an additional test may be ordered to gain confirmation. CVS, or chorionic villus sampling, involves inserting a small tube into the abdomen or the cervix in order to collect a sample of amniotic fluid. There is a small chance of miscarriage from this procedure, so it must be determined if the possible benefits outweigh the risks.

Prenatal genetic screening performed during the second trimester involves blood testing, which will determine whether the baby has an increased risk of being born with Down syndrome, trisomy 18, or spina bifida. Spina bifida is a medical condition in which the spinal canal does not completely close before birth. This can lead to difficulty walking or controlling bowel and bladder function as the child gets older.

If the blood tests during the second trimester indicate the need for further testing, a procedure known as an amniocentesis may be ordered as another method of prenatal genetic screening. This test involves inserting a needle into the placenta through the abdomen in order to collect amniotic fluid for further testing. Complications, including miscarriage, are a possibility with this test as well, so the parents should make an informed decision before consenting to the test.

During the third and final trimester of pregnancy, there are no typical prenatal genetic screening tests performed. However, an ultrasound may be used to check for visible abnormalities. Any questions or concerns should be discussed freely with the doctor prior to the birth of the baby.