Babies Tale

This is a routine blood test carried out at between 16 and 18 weeks of pregnancy. It measures the level of a substance called alpha-fetoprotein (AFP), which gets into the mother’s bloodstream from the baby. A high level of alpha-fetoprotein can mean a number of things: that the pregnancy is further advanced than was thought, that the mother is expecting twins, or that the baby is suffering from a neural-tube defect. It can also mean nothing at all!

If a woman does have a higher-than-normal level of AFP, a second blood test will be done to confirm it. If this test is positive also, there is a roughly l-in-7 chance the fetus has a neural-tube defect. It is usually recommended that the woman have an ultrasound scan to check for the presence of anencephaly or spina bifida. If results are inconclusive, an amniocentesis is usually recommended so that the level of AFP in the amniotic fluid can be measured (see section below).

The problem with the AFP blood test is that for every ten women with a raised AFP level, only one will have a cause found for it. The other nine will have a normal baby, although they may have a slightly greater risk of having a small-for-dates baby. The majority of women with a high AFP level will have a “positive” result and then an amniocentesis performed, accompanied by a lot of stress and worry, when there is actually nothing wrong with their baby. The chance of the AFP level being high from other causes is greater than the risk of a neural-tube defect.

Rather than perform the AFP test routinely without fully consulting the mother, healthcare professionals might do better to explain what the test is for, what it involves, and let the mother choose whether to have it. Some people welcome the test, but others prefer to do without it.

“I had just had the scan, seen the baby moving [and] that its head was there and it was kicking its legs. I thought we would have seen if there was anything really wrong. Its head would have been the wrong shape or its legs paralyzed. Anyway, I couldn’t possibly have aborted that baby once I had seen him like that. So I decided not to have the test. What was the point of having it done when I could see there was nothing so wrong with the baby and I wouldn’t have wanted an abortion anyway?”

Besides, not all neural-tube defects are detected by the test.

There is no absolute level of AFP in the amniotic fluid at which one can say, “This baby is affected and this one isn’t.” An artificial line has to be drawn. If the level is set too high, more neural-tube defects will go undetected. If it is too low, more women will have further tests with all the worry that goes with it.

A new test known as the triple-screen test has been developed.

A blood test is taken at 16 weeks and levels of alpha-fe top rote in are measured, together with two other “markers,” unconjugated estriol and human chronic gonadotropin (HCG). High levels of AFP may indicate higher likelihood of a baby with spina bifida, while low levels of AFP and unconjugated estriol, together with high levels of HCG, and indicate a higher risk of having a baby with Down syndrome.

Results from the test are combined with the woman’s age to give her a “risk factor.” A risk of one in 250 or higher is considered “screen positive”-that is, an amniocentesis or further screening is advised. A risk of less than one in 250 is considered “screen negative.” However, a positive result means, on average, only a 1-in-50 chance of the woman having a baby with Down syndrome. Again, some experts are concerned that this test will put too many women under great stress who don’t need to be by receiving a “positive” test result and having an amniocentesis.

In a more refined version of the test, called the quad-screen test, a fourth marker is measured in the blood, neutrophil alkaline phosphatase. This makes the test even more accurate at determining whether or not a fetus may have Down syndrome.

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