When 32-year-old Shelley Roberts of Sacramento, California was contacted by a nurse from her obstetrician's office calling to reveal the results of her recent blood test she immediately handed the phone off to her husband. Roberts, the mother of a three-year-old son, could not bear to hear that her blood test had come back abnormal, suggesting her unborn child had a risk for possible birth defects.
Anayat Durrani

"I was completely devastated. My test had come back 1/78 for Down Syndrome and they couldn't get me an appointment with the genetic counselor for two weeks," says Roberts. "Those two weeks were the hardest. I didn't sleep, eat or live."

Thirty-three-year-old Angela Williams of San Antonio, Texas, got the call at work. "I was told by the nurse 'Your baby tested positive for Downs.' I was speechless, and in total shock," she says. "Needless to say, I left work early that day in tears, calling my husband with the sad news."

What is the AFP test?
The Alpha-fetoprotein test (AFP) is a blood test given to women in their second trimester of pregnancy, usually between weeks 15 and 20. When a woman is pregnant, alpha-fetoprotein is produced by the fetus and mixes with the mother's blood. Alpha-fetoprotein can be detected in a blood sample taken from the arm, according to the Division of Research at Kaiser Permanente, a healthcare system in Northern California.

A high level of AFP can be an indication of a neural tube defect such as spina bifida. However, high levels of AFP can also indicate that the mother is further along in her pregnancy than realized and her due date needs to be recalculated. A high AFP could also mean the mother is carrying twins, according to Kaiser Permanente.

A low level of AFP can be an indication of genetic defects such as a higher risk of Down Syndrome (Trisomy 21) or Trisomy 18, a more severe and less common chromosomal anomaly.

Most AFP tests now also include testing of two or three more markers, says Dr Harold N. Bass of the Department of Genetics at Kaiser Permanente Medical Center in Panorama City, California. The triple marker test, also known as the multiple marker, measures levels of AFP, hCG and estriol. The quad screen measures the same as the triple, as well as another marker called Inhibin.

"In California, triple marker screening, with a screen-positive rate of 5.6 percent, has an overall Down Syndrome detection rate of 66 percent. The detection rate for Trisomy 18 is 60 percent and for open neural tube and abdominal wall defects, 80 to 97 percent," says Dr Bass, clinical professor of human genetics and pediatrics at the David Geffen School of Medicine at the University of California, Los Angeles.

Dr Bass says the expanded AFP screening, as it is called in California, is required by law to be offered to all pregnant women in the state. Patients in California are given the option to refuse the test and the follow up services. Most other states do not require that AFP/multiple marker screening be offered.

Positive/abnormal AFP
Once a patient receives an abnormal or positive AFP result they are then advised to schedule an appointment to see a genetic counselor, a health professional with a specialized graduate degree and experience in medical genetics and counseling.

"When I see a patient who had a positive screen for one of these conditions, I explain the difference between a screening test and a diagnostic test. A positive screening test does not mean that there is a problem, it only means that further testing is warranted," says Diane Masser-Frye, a certified genetic counselor at the University of California, San Diego Center for Fetal Diagnosis. "Traditionally, about 5 percent of women who take the AFP test will get a positive result, but more than 90 percent of those will go on to have normal babies."

When a patient meets with a genetic counselor a family history is plotted to determine if further testing is needed. The genetic counselor also explains the option of having a level II ultrasound which uses sound waves to give a detailed examination of the fetus and an amniocentesis, which is a test of the fluid that surrounds the fetus in the womb.

"Genetic counseling is helpful for patients so they can understand their testing choices, the risks they involve and other options they have," says Masser-Frye.

False positives
Williams, whose ultrasound and amnio results came back normal, says her only complaint has been that she wished her doctor had given her more information about the AFP test and the option of not taking it in advance. "We have tried to just put the bad experience behind us and focus on [the birth of] our healthy girl."

AFP tests can sometimes be wrong. This is called a false positive. One of the major complaints about the AFP test has been what is perceived as a high rate of false positives. "The screen-positive rate is not unacceptably high for a screening test," says Dr Bass. "Without such a rate, the screening test would pick up far fewer fetuses with Down Syndrome, Trisomy 18 or neural tube or abdominal wall defects."

When an ultrasound and amniocentesis returns normal, there are other explanations as to why a patient could have received an abnormal AFP test.

"An 'unexplained' elevated maternal serum AFP level might signify potential pregnancy complications down the line, such as maternal hypertension, preterm birth and poor fetal growth," says Dr Bass.

Roberts' case proved to be a false positive. She gave birth to a healthy baby girl by C-section. After having gone through months of stress and constant worrying, Roberts says it was all worth it. But would she take the AFP test again? "I myself would take the test again. Just to know if there is the possibility of a problem."

Genetic counselor Masser-Frye believes the AFP test should be available to all women should they chose to take the test. "I do recommend the AFP test for women who feel like they want to know about Down Syndrome, Trisomy 18 or spina bifida prior to delivery," she said. "For women who would prefer not to have any kind of prenatal diagnosis, taking the AFP is not necessarily helpful."PregnancyAndBaby.com

recommended for you