What types of tests are done during pregnancy?
A number of tests are recommended for all women as part of prenatal care. Some of these tests are carried out on blood and urine samples and on cells from your cervix and vagina. You will also be tested for infections, including sexually transmitted infections (STIs). The results of these tests are used to check for possible problems that may affect you or your baby. Many problems, if found, can be treated during the pregnancy. Some tests are done to find out whether you or your baby are at risk of certain problems; these are called screening tests. They may be offered on the basis of your age, your history or your ethnic background.
Other tests are done to find problems that may arise during your pregnancy. These are called diagnostic tests. They may be offered on the basis of your medical history, your family background, your ancestry or the results of other tests.
What types of blood tests are given during pregnancy?
Blood tests are done to check the following:
- Blood group and antibody screen — your blood type may be A, B, AB or O. It may be Rh positive or Rh negative.
- Hematocrit and hemoglobin — the levels of these two are measured to check for anemia.
- Rubella — your blood will be checked for signs of previous infection with German measles (rubella).
- Hepatitis B virus.
- Syphilis.
- Human immunodeficiency virus (HIV).
- Glucose — your blood sugar level is measured to check for diabetes.
- Cystic fibrosis carrier screening
Why is my urine tested?
Your urine may be tested at each prenatal visit. This test checks the levels of sugar and protein in your urine. Although the presence of sugar in the urine is normal in pregnancy, high levels could be a sign of diabetes. Protein in the urine may be a sign of a urinary tract infection or kidney disease. In late pregnancy, it can be a sign of preeclampsia. If these problems occur, they can be treated.
What options are available for screening for birth defects?
Screening tests can be performed in the first trimester, second trimester, or both trimesters (the results of first- and second- trimester test results are considered together). Carrier testing also is an option before and during pregnancy. Carrier testing checks whether one parent is a carrier or both parents are carriers of certain inherited disorders. Cystic fibrosis carrier testing is available for all pregnant women. Other carrier tests are recommended for people of certain ethnic backgrounds or those who have a strong family history of a genetic disease.
What tests are included in first-trimester screening for birth defects?
First-trimester screening for birth defects includes blood tests and an ultrasound performed between the 11th and 14th week of pregnancy. These tests assess the risk of Down syndrome and trisomy 18. The screening can be done as a single, combined test or as part of a step-by-step process. The ultrasound examination, called the nuchal translucency scan, is used to measure the thickness of the skin at the back of the baby's neck. An increase in this space can be a sign of Down syndrome, trisomy 18 or other problems. The blood tests measure the level of two substances in the mother's blood, called pregnancy-associated plasma protein A and human chorionic gonadotropin. Abnormal levels of these two proteins can be a sign of Down syndrome.
What tests are included in second-trimester screening for birth defects?
In the second trimester a test called multiple marker screening is offered to screen for Down syndrome, trisomy 18 and neural tube defects. This test measures the level of three or four of the following substances in your blood:
1. Alpha-fetoprotein (AFP) — a substance produced by a developing baby, which is found in the amniotic fluid, in the baby's blood and, in smaller amounts, in the mother's blood.
2. Estriol — a hormone produced by the placenta and the baby's liver.
3. Human chorionic gonadotropin
4. Inhibin-A — a hormone produced by the placenta.
The test that uses the first three substances is called the triple screen. The test that uses all four is called the quadruple screen.
If I am at risk of having a baby with a birth defect, what tests may be performed?
If the screening results show that there is an increased risk of having a baby with a birth defect, the following diagnostic tests can be done:
- Amniocentesis — for this test a small amount of amniotic fluid and cells is taken from the sac surrounding the baby and tested. This test is done in the second trimester of pregnancy.
- Chorionic villus sampling (CVS) — for this test a small sample of cells is taken from the placenta and tested. This test is done in the first trimester of pregnancy.
- Ultrasound — this type of ultrasound examination gives a detailed picture of the baby's organs and features.
Both amniocentesis and CVS carry a small risk of pregnancy loss. Your doctor can explain these risks to you.