Prenatal Genetic Testing and Screening

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Prenatal genetic testing and screening are two ways to determine whether your unborn baby is at risk of having a genetic disorder or has one.

Genes are the hereditary material in your body called DNA that control your unique physical makeup and how your body functions. You get half your genes from your father and half from your mother. Chromosomes are the structures inside the cells in your body that carry the DNA. You have 23 pairs of chromosomes, or 46 total.

Genetic disorders are caused by abnormalities with genes or chromosomes, either in the way they combined after the sperm fertilized the egg or because one or more genes is abnormal in itself.

Sometimes babies are born with extra or missing chromosomes, called aneuploidy, that cause unusual physical and cognitive characteristics. The most common aneuploidy is a trisomy, where there are three of a particular chromosome instead of a pair.

The most common of these are:

  • Down syndrome (also known as Trisomy 21): A chromosomal disorder that causes abnormal face and body features, medical problems such as heart defects, and some cognitive disabilities. Most babies born with this disorder live into adulthood.
  • Trisomy 18 (also known as Edwards Syndrome): A chromosomal disorder that causes severe intellectual and physical disabilities. Most babies with this disorder die before birth or within the first month of life, although a small number live into adulthood.
  • Trisomy 13 (also known as Patau Syndrome): A chromosomal disorder that causes serious problems with the brain and heart and other physical defects. Most babies with this disorder die within the first few days or weeks of life.

A baby may also be born with an inherited disorder, which is caused by defective genes that are passed down from the parents. Examples of inherited disorders include cystic fibrosis and sickle cell disease.

Three Types of Genetic Testing and Screening

Carrier Screening

If certain genetic disorders run in your family or your partner’s, a carrier screening blood test can detect if either of you carry a gene that causes that disorder that you might pass on to your baby. Ideally, this test is done before you become pregnant, but it can be performed at any time. Some inherited disorders can be passed on to your baby if one parent carries the gene, and for some, both parents must carry the gene.

Prenatal Screening Tests

These screening tests can tell you the chances that your unborn baby will have certain genetic disorders, but they cannot tell you if your baby has them for sure. Different tests screen for different conditions and are conducted at different times during pregnancy.

First-Trimester Screening

Timing: 10 to 13 weeks pregnant

Method: blood test and ultrasound exam

Screens for:

  • Down syndrome
  • Trisomy 18

Second-Trimester Screening

Timing: 15 to 22 weeks pregnant

Method: blood test

Screens for:

  • Down syndrome
  • Trisomy 13
  • Trisomy 18
  • Neural tube defects, which are birth defects that result from the incomplete development of the brain (anencephaly), spine (spina bifida), or spinal cord

Integrated Screening and Sequential Screening

Timing: 10 to 22 weeks pregnant

Method: Blood test that is a combination of the first-trimester and second-trimester screening

Screens for:

  • Down syndrome
  • Trisomy 13
  • Trisomy 18
  • Neural tube defects

Cell-Free DNA Screening

Timing: 10 weeks pregnant or more

Method: Blood test, which works best for a woman whose baby is at high risk for a genetic disorder or who has had a previous positive screening test result

Screens for:

  • Down syndrome
  • Trisomy 18

Standard Ultrasound Exam

Timing: 18 to 22 weeks pregnant

Screens for physical birth defects:

  • Brain and spine
  • Face
  • Abdomen
  • Heart
  • Arms and legs

Diagnostic Tests

Diagnostic tests can tell you whether your baby actually has certain genetic disorders or specific inherited disorders. Because these tests involve disrupting the baby’s safe environment inside your uterus, they carry a very small risk of resulting in a miscarriage. This is something to consider before deciding to move forward with this kind of test.

Chorionic Villus Sampling

Timing: 10 to 13 weeks pregnant

Method: Your doctor takes a small sample of chorionic villi, which are growths on the placenta that have the same genetic makeup as the baby, to test them for abnormalities. There is a slight chance of miscarriage as the result of taking the tissue to do the test.

Detects:

  • Down syndrome
  • Trisomy 13
  • Trisomy 18
  • Inherited disorders for which you request testing

It does not detect neural tube defects.

Amniocentesis

Timing: 15 to 20 weeks pregnant but can be done any time up until you give birth.

Method: The doctor uses a thin needle to draw out some of the amniotic fluid that surrounds the baby and tests the fluid. There is a very small chance of a miscarriage following the test.

Detects:

  • Down syndrome
  • Trisomy 13
  • Trisomy 18
  • Inherited disorders for which you request testing
  • Some types of neural tube defects

We offer all patients the opportunity to have genetic screening or testing. Some parents want to know if their baby will have a genetic disorder because they want to be prepared. Some parents don’t want to know. There is no right or wrong – it’s the choice of every family to make.

If you are planning to have a baby, you may want to talk with your partner and your doctor about carrier screening if you are concerned about your family health history. Once you are pregnant, your doctor will talk with you about prenatal screening or testing, but feel free to ask about it at any time.

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Cheyenne, WY 82001

We are located at the corner of Parkview and College,
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