I just received a high reading on my AFP test, and no one seems to want to tell me what this means. I am scheduled to see a specialist in a few weeks, but what I have read is not good news. What does this mean? What are the odds of birth defects?

--Natalie

An abnormality on alpha-fetoprotein (AFP) screening (a test of a pregnant woman's blood done between 15 and 20 weeks of pregnancy) should be investigated within days, not weeks. Many times an abnormal result is due to an error in calculating the gestational age (how many weeks you are pregnant). A normal reading for 15 weeks is abnormal at 16, so if you were not exactly as many weeks along as was thought -- and was indicated on the test form -- then the result will be reported as abnormal.

The first step, therefore, in evaluating an abnormal AFP is to have an ultrasound (if one has not been done already) to confirm gestational age. If indeed gestational age was wrong, the correct information is given to the lab that read the AFP test, and it is determined whether the AFP reading is actually okay for the true gestational age. A high AFP can also result if you are carrying twins. Again, an ultrasound can determine this, and once again this information is passed on to the lab for a corrected reading.

Hernias in the baby's abdominal wall (omphalocele, gastroschisis) and intestinal or urinary obstruction may produce abnormally high AFP levels; these abnormalities may often be detected on detailed "level II" or "targeted" ultrasounds. Neural tube defects such as spina bifida (in which the baby's spinal cord and spinal column do not close properly) and anencephaly (in which the skull and brain do not form properly -- a condition that is incompatible with life) are associated with high AFP levels. An ultrasound will detect anencephaly, but it may miss subtle cases of spina bifida. Passage of fetal blood into mom's circulation, as may happen with a threatened miscarriage, may also elevate AFP.

About 2.5 to 5 percent of women tested will initially have a high AFP, but if the test is repeated, almost 30 percent of these women will then test normal. If AFP is persistently elevated, an ultrasound is done to confirm gestational age, rule out twins (or more!) and look for obvious defects like anencephaly. If this first ultrasound is normal, a targeted ultrasound is done by a maternal-fetal medicine specialist (perinatologist). If the targeted ultrasound does not reveal any abnormalities, then amniocentesis is performed to directly measure the level of AFP and acetylcholinesterase in the amniotic fluid; elevations of acetylcholinesterase are associated with neural tube defects. Chromosomal analysis of the baby is sometimes done as well from the fluid obtained during an amniocentesis.

About 1-2 percent of the time, the reason for a high AFP cannot be determined -- all testing shows a normal pregnancy. Studies have indicated that these should be followed as high-risk pregnancies because complications such as low birth weight, stillbirth, preterm delivery and placental abruption are increased.

I would encourage you to have an ultrasound NOW. Most likely you will find your dates are off, the AFP will be recalculated, and you will be reassured. If not, you should be offered a targeted ultrasound; in my area, we can get a patient into see the maternal-fetal medicine specialist within a few days under these circumstances (and our closest specialists are 60 miles away and there are only two of them!). You should not have to wait a "few weeks" to have a high AFP investigated!