If you're 35 or older, you probably know that you have a higher risk for pregnancy problems. To help rule out any concerns, your doctor may offer you some additional prenatal tests. Whether you want to have these tests is up to you.
- You'll gain peace of mind about your babies' health.
- You can learn about and prepare for your babies' special needs if a genetic problem is found.
- You can use the information to help make decisions about how best to care for your pregnancy.
Not all tests are without risks, and sometimes tests can have false results. Talk with your doctor about the risks, benefits, and limitations of each test so you can make the best decision for you. Here's an overview of the tests you may be offered.
Moms of all ages usually have one or more ultrasounds during their pregnancy. This safe test uses high-frequency sound waves to produce an image of your babies. An ultrasound may be used to:
- Confirm that you are pregnant
- See if you are carrying more than one baby
- Determine whether your babies' hearts are beating
- Estimate your babies' due date and see how your babies are growing
- Determine your babies' genders
- Examine your ovaries and uterus
- Determine the location of the placenta and the amount of amniotic fluid
- Look for signs of birth defects such as cleft lip, heart defects, spina bifida, and Down syndrome
First Trimester Screen
This test is done between weeks 11 and 14. It involves a blood test and an ultrasound.
- The blood test measures two markers in your blood.
- The ultrasound measures the thickness of the back of your babies' necks.
Taken together, the results look for problems with your babies' chromosomes, such as Down syndrome.
This test serves the same function as the quad marker screen (below), but allows your doctor to see your babies. It also tends to cause fewer false alarms. Sometimes it's combined with a second blood test like the quad screen, to give a result that is more accurate than either of the individual tests.
Quad Marker Screen
A quad marker screen is a blood test performed between the 15th and 20th weeks of pregnancy. It measures substances in the blood that may show:
- Problems with a baby's brain and spinal cord, called neural tube defects. These include spina bifida and anencephaly. The quad marker screen can detect about 75% to 80% of neural tube defects.
- Genetic disorders such as Down syndrome. The test can detect about 75% of Down syndrome cases in women under age 35 and more than 80% of Down syndrome cases in women 35 and older.
It's important to know that the quad screen only indicates your level of risk for birth defects. If the test shows a risk greater than the average risk of a 35-year-old woman, then the test is considered to be positive. The test can't diagnose birth defects, so a positive result doesn't mean that your babies have a birth defect. In most cases, the babies are healthy despite an abnormal test result.
If the test is positive, your doctor may suggest having diagnostic tests, such as:
- Amniocentesis to check your babies' chromosomes
- Ultrasound to look for signs of birth defects
Unlike blood testing, which only shows whether you are at risk, amniocentesis is used to make a diagnosis. During the test, your doctor will insert a needle through the abdomen wall, using ultrasound images to help guide the needle into the uterus. He or she will remove a small amount of amniotic fluid from the sac(s) surrounding your babies. This sample is then used to check the babies' chromosomes and test for genetic diseases. In addition to the most common chromosome problems, including Down syndrome, trisomy 18, trisomy 13, and Turner syndrome, the sample can also be tested for:
Chorionic Villus Sampling (CVS)
CVS is an alternative to amniocentesis, and it can be performed earlier in the pregnancy. Like amniocentesis, CVS can diagnose some diseases. If you have certain risk factors, you may be offered CVS as a way to detect birth defects during early pregnancy.
During this test, a small sample of cells, called chorionic villi, is taken from the placenta. Chorionic villi are tiny parts of the placenta that are formed from the fertilized egg, so they have the same genes as your babies. To get the cells, a doctor passes a needle through the vagina or the abdomen, depending on the location of the placenta. The cells are used to check your babies' chromosomes, just like amniocentesis.
CVS and amniocentesis usually involve genetic counseling, where you speak with a counselor about your risk for genetic disorders. You will also learn about the risks and benefits of the procedures. Because of the risks associated with CVS with a twin pregnancy, it is not commonly done.
Noninvasive Prenatal Diagnosis
This new blood test, also called cell-free DNA testing, is used to show whether you are at risk for having babies with chromosome problems. Because it's done by using a sample of your blood, it's less invasive than amniocentesis or CVS.
The test finds a baby's DNA floating around in the mother's blood. The result determines the chance that the baby could be born with Down syndrome, trisomy 18, or trisomy 13.
Using this test in twins remains controversial. Ask your doctor or genetic counselor if this test is appropriate for you.