Prenatal Testing

Here's an in-depth look at the screening and diagnostic tests you might undergo, and how some real couples dealt with the decisions and emotional issues involved.

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Prenatal testing can be a multi-edged sword. Usually, test results are reassuring, which puts expectant parents' minds at ease. But some people argue that because birth defects are rare, these tests in most cases cause undue stress; others argue that they allow people to create "designer" children. Then there are the parents who discover very real, sometimes dire, problems with their babies and face the decision of whether to keep or terminate a pregnancy. Testing is a difficult and confusing issue, and what's right for one family may be entirely wrong for another.

Some women opt out altogether, claiming that even if a problem were detected, they would never terminate a pregnancy. Others choose to undergo blood screening tests but nothing invasive, such as amniocentesis. Still others say yes to every procedure offered to them, wanting to gather as much information as possible about the fetus's health—and, hopefully, reduce their anxiety along the way.

"Testing is a very sensitive issue, and a very personal one," says Barbara M. O'Brien, M.D., a geneticist and maternal-fetal medicine specialist at Women & Infants Hospital in Providence, R.I. "Patients can feel pressured to opt into screening, but they shouldn't be. It's a personal decision."

The topic can be so delicate that prospective parents should start considering it very early, even when they begin planning a pregnancy. "The clock is ticking once you conceive," explains certified nurse-midwife Barbara L. McFarlin, Ph.D., C.N.M., of the department of women, children and family health science at the University of Illinois at Chicago College of Nursing. "There are certain windows when tests have to be completed." Following are the most common screening and diagnostic tests currently being given, along with a few other types most moms-to-be have. But which you are offered, and which you choose to undergo, may vary according to your age, where you live, your personal or family history, and many other factors.

3 Types of Tests and What They Can Tell You

Screening Most women are offered a screening test in both the first and second trimesters. Your results will come back as either "screen positive" or "screen negative," along with a specific risk. "A screening test will never give you a 'yes' or 'no' answer," says genetic counselor Cathy Wicklund, M.S., C.G.C., director of the graduate program in genetic counseling at Northwestern University in Chicago. "All they can do is quantify risk."

Every woman interprets risk differently based on her personality, her education level, even the way information is presented to her. But perhaps most influential is her life experience. "If you're the one person who got struck by lightning, you're going to think that in a 1-in-100 risk scenario, you're going to be that one," Wicklund says.

Diagnostic Unlike screening tests, diagnostic tests can confirm a birth defect exists by studying tiny samples of a fetus's genetic material. Approximately 5 percent of women are referred for diagnostic tests following screening; O'Brien says the incidence of diagnostic tests is decreasing because of improved screening tests.

Routine In addition to the tests described here, you'll likely undergo a urine test at each prenatal visit to check for bacteria, which could signal a urinary-tract infection, and protein, a potential preeclampsia symptom.

Blood Work

This is usually done at your first prenatal appointment to screen for certain diseases, including STDs, and determine your blood type.

Chorionic Villus Sampling (CVS)

Who it's offered to: Women who will be older than 35 at delivery; those who have an abnormal first-trimester screening test result.

When it's offered: At 10 to 12 weeks.

What it screens for: Down syndrome and some other chromosomal defects.

How it works: A small piece of tissue is taken from the placenta via a tube inserted through the cervix or a needle inserted through the uterine wall.

How effective it is: Almost 100 percent. It poses a miscarriage risk of approximately 1 percent.

What if ...? If a defect is diagnosed, you'll need to decide whether to continue the pregnancy.

First-Trimester Screening

Who it's offered to: All women.

When it's offered: At 10 to 13 weeks.

What it screens for: Chromosomal defects such as Down syndrome and trisomy 18 (an often lethal defect); some cardiac defects.

How it works: Blood is drawn from the mother, and three fetal proteins are measured. These results are combined with the results of a detailed ultrasound (nuchal translucency) that measures the thickness at the back of the fetus's neck.

How effective it is: It has an 80 percent to 85 percent detection rate for Down syndrome, with a 4 percent to 6 percent false-positive rate.

What if ...? If you have a positive screen and are not comfortable with the odds, you may opt for a diagnostic test to determine if your baby has a defect. Another option is to do an additional screen in the second trimester—but this will not give you a definitive answer, either.

Full Integrated Screen

Who it's offered to: All women (if it's available in the area where she lives).

When it's offered: The first part is conducted at weeks 10 to 13; the second part, at weeks 14 to 20.

What it screens for: Down syndrome.

How it works: Results from the first-trimester ultrasound and blood work are combined with the results from second-trimester blood work.

How effective it is: "It has a very high detection rate for Down syndrome—85 percent to 90 percent—with a very low false-positive rate: 1 percent to 2 percent," O'Brien says.

What if ...? If you do have a positive screen, you'll need to decide if you'll have amniocentesis to confirm the diagnosis (it's too late for CVS).

Second-Trimester Screening

Who it's offered to: All women.

When it's offered: At 14 to 20 weeks.

What it screens for: Down syndrome, trisomy 18 and neural-tube defects (NTDs) such as spina bifida.

How it works: Consists of a blood test that typically looks at four different proteins in the mother's blood; often referred to as the "quad screen" or "multiple marker screening." Unlike first-trimester screening, second-trimester tests can screen for NTDs in addition to chromosomal defects such as Down syndrome.

How effective it is: It has an 80 percent to 85 percent detection rate for Down syndrome, with a 7 percent false-positive rate.

What if ...? If you have a positive screen for any defect, you may choose to have an amniocentesis; a level II ultrasound may also be offered.


Who it's offered to: Women who will be older than 35 at delivery; those who have an abnormal first- or second-trimester screening test result.

When it's offered: At 15 to 20 weeks.

What it screens for: Chromosomal defects such as Down syndrome; developmental defects such as NTDs.

How it works: A small amount of amniotic fluid is extracted via a needle inserted through the abdomen and uterus.

How effective it is: Almost 100 percent. The risk of miscarriage from the procedure is approximately 1 in 200 to 1 in 600, depending on the skill and experience of the person performing the procedure.

What if ...? If a defect is diagnosed, you'll need to decide whether to continue the pregnancy or terminate it.


Who it's offered to: All women.

When it's offered: At about 20 weeks (also offered as part of the first-trimester screening).

What it screens for: A wide variety of problems. "An anatomical survey of the entire fetus is typically conducted," explains midwife Barbara McFarlin.

How it works: Using a transducer placed over the abdomen, sound waves create pictures of the fetus.

How effective it is: McFarlin says it detects approximately 50 percent of heart defects; O'Brien says it's excellent at detecting NTDs. However, O'Brien adds: "Fifty percent of babies born with Down syndrome had normal ultrasound results."

What if ...? If ultrasound does detect a potential problem, you'll need to decide if you want an amnio to determine whether it could be part of a chromosomal or genetic syndrome.

Glucose Screen

This test is done at weeks 26 to 28 to check for gestational diabetes (high blood sugar during pregnancy), which increases the risk of having a too-large baby and needing a C-section.

Group B Streptococcus

At 36 weeks or so, you'll be tested for the presence of potentially dangerous bacteria that could be passed to the baby during delivery. It involves a painless swab of your rectum and vagina.

Issues to Consider

Perhaps the biggest issue surrounding prenatal testing is what you would do if a problem were detected.

"Women think they have to terminate, but that's not true," McFarlin says. "You can continue the pregnancy and use that time to educate yourself about the baby's condition, talk to other families dealing with the same issue, maybe even prepare for the delivery." For instance, if the baby will need surgery for a heart malformation at birth, you can find a hospital with that capability and deliver there.

Testing involves many such big decisions—ones that your doctor may not be able to discuss at length. "A discussion about prenatal testing can take up to an hour, time that many doctors just don't have," O'Brien says, adding that knowing all the details of the various tests may not even be within their area of expertise. As a result, many doctors routinely refer patients to a genetic counselor, who specializes in this area. One important note: If a diagnostic test indicates a problem, get a second opinion from a perinatal (high-risk) specialist.

Real-Life Decisions

Choosing Not to Test: "I feel like knowing about a problem before you have the child and can do anything is torture."

Even though she was going to be 39 when her baby was born, Liz Lane and her husband, Brent, decided at the outset that they wouldn't do any prenatal testing. Not only were they confident that they would not terminate a pregnancy under any circumstances, but Liz felt that if they did find out about a problem, her pregnancy would be marred by sadness and stress.

Their doctor advised the San Diego-area couple to meet with a genetic counselor to discuss their risks, but they decided against this, too. They did, however, have an ultrasound. "We wanted to find out the gender, and the doctor wanted to check on same basic things, such as whether the cord was wrapped around the baby's neck," Liz says. "But I told him that if he found a genetic or other problem, we didn't want to know."

The doctor did tell the Lanes that if he were to detect a problem that would require special care after delivery, he would be beholden to let them know. But he found nothing wrong, and baby Robin was born full term, in perfect health, in January 2010.

Working with Limited Information: "It was very scary, and we immediately starting having this what-will-we-do-if-there's-something-wrong talk."

Northern California couple Sheila and Ethan Cooperman (not their real names) were expecting their first child, and they decided to have an amniocentesis at 16 weeks because of Sheila's age, 35.

"The doctor called 2 ½ weeks after the test and told us there was an abnormal test result and we needed to come in to discuss it," Sheila says. The Coopermans were told that a genetic mutation had occurred in about 15 percent of the baby's cells, yet it couldn't be determined how severe any effects would be. "We knew something had gone wrong, but we didn't know what," Sheila says. "If the cells affected were in the brain, the baby could be severely retarded. If they were in the elbow, the baby could have a big mole."

Because no other diagnostic tests were available, Sheila and Ethan opted to have a detailed ultrasound. While waiting for the appointment, they started doing some serious soul-searching. "Those three days were hell," Sheila recalls. "We had to have discussions like what if the baby has one arm and two legs? No arms and no legs? Mental retardation?" The couple eventually decided that if they thought their child had a chance at happiness, they would continue the pregnancy.

The ultrasound showed no obvious defects, and today their daughter Renee is 13 and completely healthy. The couple always have a bit of fear hanging over their heads about what might unfold in the future. "But when Renee was born, we vowed that we would rejoice in normal," Sheila says. "If she had tantrums, if she was an average student, whatever: Hallelujah!"

A Heartbreaking Decision: "It was incredibly difficult for both of us, but we felt the only thing we could do was terminate."

Rhonda Berg, then 32 and pregnant with her first child, had a screening test at 16 weeks, and the results indicated that the baby had a slightly elevated risk of a neural-tube defect. Even though he assured her that everything was probably just fine, her doctor recommended that she get an ultrasound and an amnio.

Before their ultrasound the next day, Rhonda and her husband, Alex, who live in Pennsylvania, met with a genetic counselor; she also was reassuring. But the reassurance was short-lived. "The perinatologist became very quiet as he did the ultrasound," Rhonda says. "Then he switched off the machine, took a deep breath and told us that he was sorry, but the baby had a very bad defect of the spine.

"I started shaking and crying," Rhonda recalls. "Alex tried to comfort me, but what could he do?" An amniocentesis confirmed that the baby had severe spina bifida, with significant brain involvement as well. "We felt the only thing we could do was terminate, but it was such a terrible, heartbreaking decision," Rhonda says.

It took two years before the Bergs felt ready to try for another baby, and for several months beforehand, Rhonda took very high doses of folic acid daily. "I was so scared to have an ultrasound during that pregnancy," she says. "But the doctor knew our history and was grinning from ear to ear when he told us our baby was just fine." Happily, the Bergs had a healthy son 12 years ago, followed by healthy twins nine years later.

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