Introduction to Prenatal Tests

Introduction to Prenatal Tests

Once you become pregnant, your doctor may order several tests. These tests are important for you and your baby.

You couldn’t imagine that first test, the one where you pee on the little stick, was just the start. After a few minutes, the plus sign appeared in the small window. If only they were all this simple. Now you pee in a cup at each doctor’s visit, but the tests don’t end there. Here’s what to expect and why prenatal tests are so important.

Prenatal tests can determine a variety of things about the health of you and your unborn baby. Tests are done throughout pregnancy. Many tests are routine and almost all pregnant women have them as part of their prenatal care. Other tests are suggested to certain women by their doctors depending on their particular needs.

Tests for mom

At your first prenatal visit, your doctor may perform a blood or urine test to confirm your pregnancy. Expect to have your urine tested and blood pressure taken at each visit. Monitoring your blood pressure and urine are quick, easy ways for your doctor to identify any problems.

Routine prenatal tests can tell a lot about the mother’s health. Tests can show if you have:

  • Gestational diabetes
  • Anemia
  • Immunity to certain diseases, such as chicken pox and rubella
  • Infections, such as sexually transmitted diseases or urinary tract infections
  • Rh incompatibility (a different blood type than the baby)

It is important to identify these conditions early so they can be treated. Treatment during pregnancy can help prevent harm to the baby.

Carrier testing (Genetic testing)

If you are of a specific ethnic background or have a family history of certain diseases, your doctor may suggest a specific type of genetic test. This can help determine whether you carry that specific disease. Even if you don’t have the disease yourself, you may still pass the gene on to the baby if you are a carrier of the gene. Fathers can be tested, too. This type of screening can check for cystic fibrosis, sickle cell and other types of genetic diseases.

Tests for baby

Other prenatal tests tell a lot about the unborn baby’s health.

Screening tests are used to see if the baby is at risk for birth defects. Common screening tests include ultrasound and blood tests. These are used to see if the baby is at risk for chromosomal abnormalities. Blood tests can check for defects such as Down syndrome. A detailed ultrasound exam allows the doctor to see if the fetal heart and other organs are forming properly. It can also confirm the gestational age. This can be done after 18 weeks.

Depending on the initial test results or other factors such as your age or family history, your doctor may suggest more testing, such as an amniocentesis or chorionic villus sampling (CVS).

  • Amniocentesis is usually done between weeks 15 and 20 of pregnancy to detect chromosomal abnormalities. A sample of amniotic fluid is taken and analyzed. Lab results are ready in 10 to 12 days.
  • Chorionic villus sampling (CVS) can be done earlier. It is also used to detect chromosomal abnormalities. The doctor takes a sample of the placenta and examines it. Lab results are ready in about one week.

These tests are not risk-free. There is a slight risk of miscarriage as a result of amniocentesis and CVS.

Why would I need a screening or diagnostic test?

While some prenatal tests are routinely advised, others might be suggested to a woman whose pregnancy is considered high risk. A high-risk pregnancy occurs when there is a potential for complications for the mother and/or baby. For example, women found to be at increased risk of having a baby with Down syndrome during first trimester screening would be offered genetic counseling and further testing.

Other common risk factors include:

  • Family history of genetic or birth defects
  • Mother has diabetes, high blood pressure, HIV or other health conditions
  • Previous pregnancy complications, miscarriages or stillbirths
  • Pregnant with multiples (twins, triplets, etc.)
  • Mother was exposed to something harmful during pregnancy (such as radiation, chemicals or certain drugs)
  • Screening tests produced abnormal results
  • Mother’s age
  • Mother is underweight or overweight
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