This article is from the Pregnancy Screening FAQ, by Lynn Gazis-Sax (firstname.lastname@example.org) with numerous contributions by others.
An abnormal result may cause considerable worry and concern. Since most
women with abnormal results will have healthy normal babies, you may decide
that the test is not worth the possible anxiety. Some statistics: about 5%
of women tested will have abnormal readings. About 90% of those will not
have affected babies, but have abnormal values because the dates were
calculated wrong, there are twins, or other reasons. So, for every 1000
women tested, about 50 will be told they have increased risk, and of the
50, about 45 or more will in fact have normal pregnancies. Some people feel
that the high level of "false-positive" readings make the test not worth
The tests are relatively cheap. However, follow-up diagnostic testing is
not. These costs may be covered by insurance.
The test itself has no risk to the baby. The only risk to the mom is pain
from the blood draw. However, if the results are abnormal, you may wish to
opt for an amnio to relieve your worries. Amnio does carry a small risk of
The test will not identify all cases of neural tube defects or Down's. The
problems for a baby with spina bifida range from the very minor to the very
severe. Generally speaking, the test detects only the more severe problems.
However, you may not be able to get exact details about the severity in any
particular case. This could lead to months of anxiety.
The AFP cannot be done until week 15 or 16, and takes about a week to get
the results. Followup amnio means even more waiting, so if termination is
decided, it will probably not happen until week 18 at the earliest. This
can be very difficult emotionally, and more difficult physically than an
early termination option with the CVS.
Addition by Dr. Tim Reynolds:
Depending on the equipment your lab has, the result may be available within
24 hours. In my lab we are aiming for a 6 hour turnaround.