Considering taking the various tests offered during pregnancy to aid in the detection of birth defects? It can be a difficult decision to make. Writer Marla Hardee Milling offers some insight into the various procedures.
Marla Hardee Milling

Difficult decision
The ultrasound technician squeezed a blob of warm gel on my belly, and then rotated the paddle in the sticky goo. Within seconds, an image appeared on the screen in front of her. I tilted my head to catch a glimpse of the life growing inside me.

She took careful measurements of the baby's head, legs and arms. (Shorter limbs may be an indicator of Down syndrome.) Unlike a regular ultrasound with its gray and white images, this one featured color -- bands of blue and red exploding on the screen as she pointed out the umbilical cord, spine and heart chambers. My husband, a wildlife biologist with expertise in GPS and digital mapping, admired the acuteness of the enhanced ultrasound.

Minutes before, we sat in a dim room exploring our options with a genetics counselor. While we didn't have a history of birth defects in our families, my maternal serum alpha-fetoprotein (MSAFP) screening test came back with abnormal levels, and my age (mid-30s) also put the pregnancy into a higher risk category for certain birth defects. My OB had given me pamphlets on amniocentesis and chorionic villus sampling (CVS).

We agonized over whether to undergo further testing and discussed options with the counselor and a neonatal specialist. We reviewed the risks of amniocentesis and CVS. My husband and I ultimately decided to forego the invasive tests because of potential risks to our child. We did agree, however, to have an enhanced ultrasound.

The technician's face revealed nothing as she left the room. An eternity passed before the neonatal physician came in, my chart in hand, and told us she could find no abnormalities. She smiled as we sagged in relief.

Screening tools
The AFP test and ultrasound are only screening tools: They may point to potential problems but cannot diagnose them. A diagnostic test, such as amniocentesis or chorionic villus sampling (CVS), can provide conclusive results for some abnormalities.

The AFP test is more reliable when combined with two other tests in what is known as a triple screen. "The triple screen combines the results of the AFP, HCG and estriol level tests," says San Diego obstetrician Suzanne M. Merrill-Nach. "As these tests vary higher or lower than normal in different conditions, it will find more babies with problems than any one test alone. For Down syndrome, AFP alone would find only 20 to 25 percent compared to the triple screen detection rate of 60 percent."

In women with persistently elevated MSAFP, high-resolution ultrasound is done, says Dr Kenneth E. Johnson, assistant professor OB/GYN of Nova Southeastern University and director of the Women's Health Center. "Anencephaly [congenital absence of most of the brain and spinal cord] is virtually 100 percent detectable. Furthermore, the likelihood of an open-neural-tube defect associated with an abnormal screening value is decreased by 95 percent or more if the ultrasound is normal and performed in a specialized center," he says.

Parents should determine whether or not they wish to know if there is a problem, says Merrill-Nach.

"Some do not want to know, and that is their option," she says. "If they do not want to know or if they would not want any diagnostic testing if the screening blood test or ultrasound is abnormal, then I advise them not to do the screening tests."

Testing is not fool-proof
"When I was pregnant, I specifically told my doctor I did not want to have an amnio," says Tina Miller of Merrill, Wisconsin. "My reasoning was simple. I would take the child God saw fit to give me and I would deal with it -- loving that child to the best of my ability. I am opposed to abortion. It was simply not an option for me. And besides, those tests have been known to be wrong, and when they are, a false positive can put a pregnant woman through months of unnecessary worry and stress."

Merrill-Nach says she doesn't believe that testing creates more anxiety than necessary, especially when the testing is appropriately explained, including advising that there is a 3 to 4 percent false positive rate.

"The tests certainly allow younger women, who would not be offered amniocentesis, to identify if they are carrying a baby with a serious problem," she says. "Also, the most common reason for a false positive test is an error in dating the pregnancy, and the ultrasound done to evaluate the abnormal screen allows correction of the estimated due date."

Johnson says in his nine years of practice, he has had more than 300 abnormal tests after which mothers had amniocentesis. All 300 of these babies were normal," he says. "I have delivered one Down syndrome infant, and it was this year. The mother was 28, and her MSAFP was normal. I have questioned many other OB/GYNs and their numbers are similar. As you can see, genetic screening with these tests is less than perfect, and more importantly, the accuracy of these tests is overestimated by the general public."

Why some women choose the tests
Paula Gillingham Bender of Honolulu, Hawaii, says having an amniocentesis put her mind at rest. "Since I had three miscarriages before my first daughter, I'm eager for any and all testing," says Bender. "When I was pregnant with Sophie, we had an amniocentesis. All the horror stories of big fat needles are unfounded. And to me, the information was vital."

Bender, now 42 and pregnant with her second child, will again request testing. "I am afraid of what all that means: bad eggs, brittle chromosomes, giving birth to a child with birth defects. The information will help us decide whether I will carry this child to term," says Bender. Marnie Holmes of Sydney, Australia says she chose to have the test because she did not want to have a baby with certain abnormalities like Down syndrome.

"I think that it would not be fair on the child or our family," she says. "If a problem had shown up in the test and we confirmed it, we would have terminated the pregnancy. It would have broken my heart to do so. Fortunately, everything was fine."

Positive test results may change delivery options
Other women choose the tests because they want to be prepared in the event of a high-risk birth. Knowledge of a problem with the baby can also aid doctors in delivery.

"There are some birth defects that, if identified prior to delivery, would affect either the method or place of delivery," says Merrill-Nach. "If a baby has a spinal cord defect, that baby might fare better if delivered by cesarean section to protect the spinal cord, probably at a center with a pediatric neurosurgeon available to attend the baby immediately."

"A baby with Down syndrome may have heart defects," she continues. "When diagnosed before delivery, cardiac ultrasound can evaluate the fetal heart and alert the doctors to have cardiac specialists available. Knowing about a problem allows planning for childcare after delivery. A mother planning to return to work may not be able to do so if the baby requires special care."

Careful consideration
Prenatal testing is a personal decision. Educate yourself about the advantages and risks of all the tests, and then discuss your concerns with your health care provider and counselors. With careful consideration, you'll be able to make the decision that's right for you and your

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