Everything You Need to Know About Prenatal Testing
Many parents wonder (and worry) about their baby's health. It's normal. Natural. After all, we all want the best of our wee ones. And we want this from day one, which is why so many expectant individuals undergo prenatal testing—or testing to determine if your baby has or may have a genetic condition.
"Prenatal genetic testing gives parents-to-be information about whether their fetus has certain genetic disorders," the American College of Obstetricians and Gynecologists says. There are two types of genetic testing—prenatal screening tests and prenatal diagnostic tests—and each works in its own way. The former helps parents risk assess before conception, while the latter can determine if the fetus has (or may have) a certain condition.
That said, before undergoing any genetic testing, it is important to know the risks. Not all prenatal tests are equal, and a New York Times report found there can be serious inaccuracies. False positives can and do occur.
- Related: Your Prenatal Testing Checklist
So what do you need to know about prenatal testing—and what are the most common diagnostic tools? Read on to learn about four common procedures and why your doctor will recommend at least one of them.
Many doctors do ultrasounds (which produce a picture called a sonogram, so the terms are interchangeable) to verify the age of the fetus, see if you're carrying more than one baby, and check for birth defects.
When Are Ultrasounds Done?
Ultrasounds can be performed at any stage of pregnancy.
How Are Ultrasounds Performed?
A doctor or ultrasound technician puts a jelly on your abdomen, presses a wand on it, and sound waves from the wand produce a picture of your uterus. It doesn't hurt, but the sonogram may be confusing to look at—your doctor can explain what they see. The doctor or technician can (and will) also look your baby over from head to toe: checking, for instance, for signs of a healthy spine and heart. They will also check the placenta, calculates the baby's approximate weight, and examines the baby's position to make sure everything looks healthy.
What Should You Do If You Receive Abnormal Ultrasound Results?
If any problems are suspected, or sometimes just for the sake of extra caution, you may get a more detailed ultrasound exam, called a targeted, comprehensive, or level II exam. It may use more sophisticated ultrasound equipment and will take longer, often more than 30 minutes.
- Related: Your Guide to Baby Ultrasound Exams
Prenatal Blood Tests, or Blood Work
When Is Prenatal Blood Work Taken?
It's usually performed at about 16 weeks.
How Is Prenatal Blood Work Drawn?
A blood sample is taken and is then measured for the levels of at least three substances (a protein called alpha-fetoprotein and two hormones) in your blood.
What Should You Do If You Receive Abnormal Blood Work Results?
Most pregnant people receive normal results and breathe a sigh of relief, but if you're one of the 10 percent with abnormal results, don't panic: Chances are the baby is fine. Because this is a screening test, many more babies are shown to be at risk than actually have problems. In fact, for every 100 individuals with abnormal results, only 2 or 3 have a baby with birth defects. In most cases, abnormal test results occur because your baby is either a few weeks older or younger than originally thought, which throws off the reading. So if you have an abnormal result, the first step your healthcare provider will take is to give you an ultrasound to recalculate your baby's age. The ultrasound will also show if you're carrying twins—another common cause of an abnormal blood test.
If your blood test was abnormal and the ultrasound didn't uncover the cause, your doctor may recommend an amniocentesis to test for birth defects. Also, because the risk of having a baby with birth defects rises as you age, your healthcare provider may want to do an amniocentesis as a precautionary measure between 15 and 18 weeks if you're over 35. Amniocentesis is fairly accurate in diagnosing chromosomal birth defects (such as Down syndrome), a wide variety of genetic birth defects (such as muscular dystrophy and cystic fibrosis), and certain malformations (such as neural tube defects or spina bifida).
When Is Amniocentesis Done?
Amniocentesis is usually performed between 15 and 20 weeks.
How Is an Amniocentesis Performed?
One or two tablespoons of amniotic fluid are extracted from your abdomen with a thin needle. Some say amnio doesn't hurt at all; others feel cramping when the needle enters the uterus or pressure during the short time the fluid is being withdrawn. One to 2 percent individuals will experience cramping, leaking amniotic fluid, or spotting after the procedure (which you should report to your doctor). Most physicians recommend that you rest for several hours after the test.
Amniocentesis does pose a small risk of miscarriage, so it's your choice whether or not to go ahead with the procedure. According to the Centers for Disease Control and Prevention (CDC), the rate of miscarriage after amniocentesis is between one in 200 and one in 400. The risk is three times higher if it's performed in the first trimester. It also carries an extremely low risk of uterine infection (less than one in 1,000), which may lead to miscarriage.
What Should You Do If You Receive Abnormal Amniocentesis Results?
The results can take two to three weeks, which is a long time to wait if you're nervous. However, the test provides you an opportunity to prepare ahead of time if there are birth defects—and in some cases, problems can be treated while the baby is still in the womb.
- Related: Should You Get Amniocentesis?
Chorionic Villus Sampling (CVS)
CVS tests for the same birth defects as amniocentesis, with the exception of neural tube defects. Both amniocentesis and CVS are more than 99 percent accurate in ruling out chromosomal birth defects and specific genetic problems. The benefit of CVS is that the results come back much more quickly than with an amnio. The drawback is that it's slightly more likely to give inconclusive results, which means you may need to get an amnio as well.
If you already have a child with a birth defect, had a previous pregnancy affected by a birth defect, or have family members with these disorders and are especially nervous about them, CVS may be something to consider.
When Is Chorionic Villus Sampling Done?
It's usually performed between 10 and 12 weeks.
How Is Chorionic Villus Sampling Performed?
In CVS, a physician takes a small piece of the chorionic villi, which are wisps of tissue attached to the uterine wall. The cells are collected either by transcervical CVS, in which a thin tube is inserted through your vagina and cervix, or by transabdominal CVS, in which a needle is inserted through your abdomen. The villi have the same biochemical makeup as the fetus and can show the majority of potential birth defects.
As with amniocentesis, some say that CVS is painless, but others experience cramping when the sample is taken. Some have some bleeding or spotting, which usually stops within a few days. Rest after the procedure and report any new symptoms to your healthcare provider. Test results take one to two weeks.
Chorionic Villus Sampling Risks
According to the CDC, between one in 100 and one in 200 women miscarry after CVS. So you may want to consider all your options before deciding to have a CVS performed.
Analyzing Prenatal Test Results
The wait for test outcomes can seem endless, but you'll probably get good news. More than 95 percent of those who have amniocentesis or CVS find out that the results don't show the disorders for which their baby was tested. A small number may learn that their baby does have a birth defect, but while this news can be devastating, prenatal diagnosis can sometimes improve the outlook for your baby, as some disorders can be treated before birth.
If the baby has a condition that can't be treated prenatally, the early diagnosis permits parents to prepare emotionally and to plan with their physician the safest timing, location, and method of delivery. This can make a difference. Studies suggest that babies with spina bifida, for instance, suffer less paralysis when delivered by C-section before labor has a chance to begin.