Prenatal Tests

Prenatal tests are important because they give your doctor a good idea of how healthy you are and what type of problems you are most likely to experience during your pregnancy. These tests help detect any problems that could result in birth defects or genetic diseases. The test results can help you make the best health care decisions before and after your child is born.

Doctors recommend some prenatal tests for all pregnant women. Only some women will need other screening tests to check for certain genetic problems.

Routine Prenatal Tests

Throughout your pregnancy, you’ll get routine exams to make sure you’re healthy. Your health care provider will check samples of your blood and urine for certain conditions, including:

She’ll also check your blood type and whether your blood cells have a protein called the Rh factor. You may also get:

  • Pap smear
  • Group B Strep screening. Your doctor will swab the skin in and around your vagina to check for this type of bacteria. This usually happens in the last month before you give birth.
  • Ultrasound. If your pregnancy is normal, you’ll have it twice, once near the beginning to see how far along you are, and the second time around 18-20 weeks to check your baby’s growth and make sure his organs are developing properly. But if you have a high-risk pregnancy, you may have additional ultrasounds.

Genetic Tests

Doctors also use prenatal tests to look for signs that your baby is at risk for certain genetic disorders or birth defects. You don’t have to have these tests, but your doctor may suggest some to make sure your baby is healthy. They’re especially important for women who have a higher risk of having a baby with a birth defect or a genetic problem. This is you if you:

  • Are over age 35
  • Have had a premature baby or a baby with a birth defect before
  • Have a genetic disorder or one that runs in your family or the other parent’s family
  • Have a medical condition like diabetes, high blood pressure, a seizure disorder, or an autoimmune disorder such as lupus
  • Have had miscarriages or stillborn babies in the past
  • Have had gestational diabetes or preeclampsia when you were previously pregnant

Some prenatal genetic tests are screening tests. They tell you if your baby has a higher risk of having a certain disorder or disease, but they can’t tell you for certain that he’ll be born with it. Other “diagnostic” tests will give you a more definite answer. Usually, you’ll get this kind after you have a positive result on a screening test.

First Trimester Screening is an early test used to detect Down syndrome or trisomy 18. The test uses an ultrasound measurement of the skin fold on the baby’s neck (nuchal translucency) and combines this with the results of  your blood test. Because this test is done between 11 and 13 weeks of pregnancy, it is called First Trimester Screening. This screening is only used to estimate the risk of Down syndrome and trisomy 18. It cannot diagnose or rule out any specific condition.

The Integrated Screening Test is a way to estimate the chance that a baby will be born with Down syndrome, trisomy 18, or an open neural tube defect. The test uses measurements from two blood tests and from your first trimester ultrasound. All of this information is combined, or integrated, with other details about you to tell you more about your developing baby.

Sequential Screen. This is similar to integrated screening, but your doctor reviews the results with you right after the first phase at 11-14 weeks. It’s not as accurate as the longer test, but it lets you know your baby’s risk earlier. If the screening finds there may be a problem, your doctor will use more tests to find out for sure. If it doesn’t find a risk, you’ll most likely get the second blood test at 16-18 weeks to be safe.

Maternal Serum Screening also know as a triple or quadruple marker test checks your blood for hormones and proteins that come from your baby or your placenta, the organ that brings him oxygen and nutrients. The test can look for three different substances (triple screening) or four (quadruple screening). Certain amounts of these mean your baby has a higher chance of having a birth defect or a genetic disease. This test happens in the second trimester, usually at 15 to 20 weeks.

Chorionic villus sampling (CVS) is a diagnostic test for identifying chromosome abnormalities and other inherited disorders. This test may be recommended by your health care provider if you or your partner has family medical histories that reveal potential risks. It’s performed between 10 and 14 weeks of pregnancy.

Amniocentesis. Amniocentesis may be recommended by your health care provider following an abnormal triple test result. Using a thin needle in your belly, your doctor will take a sample of the fluid that surrounds your baby and check it for genetic disorders or birth defects. The procedure takes about 45 minutes and does carry some risk. About 1 in 300 to 500 women will miscarry because of amniocentesis. Your doctor can tell you if it’s important for you to have this.

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