Down syndrome is a genetic condition that occurs when an individual inherits an extra copy of the 21st chromosome. When three copies of a chromosome are inherited, an individual is said to have a trisomy disorder. This extra chromosome changes the growth and development of a fetus as well as the mental development of an individual.
Parents-to-be who wish to know more information about their pregnancy or who wish to prepare for the birth of their child may be wondering how physicians diagnose Down syndrome.
Diagnosing Down Syndrome Before Birth
Because of the increase in women who are waiting until later in life to begin a family, more and more women are being offered Down syndrome testing during pregnancy. Screening tests may reveal that there is a chance that a baby has Down syndrome and may indicate that further testing is necessary. Other tests provide diagnostic results and are referred to as diagnostic tests.
Non-invasive prenatal genetic testing is a screening test that analyzes the risk a mother has of carrying a baby with Down syndrome. As the fetus grows, cells from the placenta are shed and released into the mother’s bloodstream. These placental cells are isolated from a blood sample from the mother and analyzed for extra chromosomes. This test can be performed as early as week 10 in pregnancy.
During the first trimester, physicians will perform an ultrasound called a nuchal translucency ultrasound. The purpose of this test is to allow the physician to measure the thickness of the nuchal translucency, a collection of fluid under the skin located at the back of the baby’s neck. Physicians know that when a baby has certain conditions, the amount of this fluid that is present increases.
During the second trimester, a triple/quadruple screening test option analyzes pregnancy-related hormones that are found in the mother’s blood. When conducting a triple screening test, physicians measure the amounts of alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG) and unconjugated estriol (uE3). When conducting a quadruple screening test, physicians measure the amounts of those three hormones as well as Inhibin A. This test is performed using a blood draw from the mother and is typically performed between week 16 and 18 in pregnancy.
Prenatal Diagnostic Testing
While screening tests assess the likelihood of Down syndrome, diagnostic testing provides definitive answers about a diagnosis.
Chorionic villus sampling or CVS is a diagnostic testing option that is available for women during the first trimester. This test utilizes a sample of the placenta in order to analyze chromosomes of the growing baby. A small amount of cells is collected from the placenta through either the cervix or the abdomen. This test is performed between weeks 9 and 11 in pregnancy.
The other diagnostic testing option used to diagnose Down syndrome during pregnancy is called amniocentesis. Amniocentesis analyzes the chromosomes of the amniotic fluid in order to detect an extra copy of the 21st chromosome. This test is conducted by collecting a sample of amniotic fluid through the abdomen between weeks 14 and 18 of pregnancy.
Diagnosing Down Syndrome After Birth
For couples who decide to forego prenatal testing, physicians will diagnose Down syndrome at the time of birth. Your physician may analyze the physical characteristics of your baby to make an initial diagnosis.
Your physician may also choose to conduct a blood test using a blood sample from the baby after birth. The chromosomes from this blood sample will be analyzed in order to determine if an extra copy of the chromosome 21 exists, confirming that your child has Down syndrome.
Working With a Genetic Counselor
If you are informed that there is a possibility that your child may be born with Down syndrome, seek help from a genetic counselor. Genetic counselors are health care professionals that will help you understand your testing options as well as help you through the emotional process of receiving results.