This article is from the Pregnancy Screening FAQ, by Lynn Gazis-Sax (email@example.com) with numerous contributions by others.
5.b No. The ultrasound exam, however. will identify the majority of defects
which cause a high AFP level. Factors such as the experience of the
ultrasonographer, the weight of the mother, the position of the fetus and
the quality of the equipment can affect its accuracy. In addition, there
are no reliable ultrasound findings for Down's.
However, Down's can be strongly suggested by an ultrasound because Down's
babies often have a certain body/face type. From one woman:
"There are, however, several characteristics that are common to Downs'
babies that a skilled ultrasound technician can look for. My technician
measured the femur (usually short in Downs' Syndrome babies), checked the
number of blood vessels in the umbilical cord (Downs' babies sometimes have
one fewer), checked the width of the forehead (usually wider for a Downs'
baby), and checked the heart (apparently, Downs' babies are more likely to
suffer from heart defects). A finding that none of these characteristics
are present does not guarantee a healthy baby, but it may provide some
reassurance, particularly in a case where the AFP reading is only
Here's some statistics about elevated AFP and normal ultrasounds:
Physician-researchers at Boston's Brigham and Women's Hospital,
after studying 87,584 pregnancies, reported that an elevated AFP
[alpha-feto-protein] level in conjunction with a normal
ultrasound scan implies a less than 0.1 percent chance that the
baby will have one of the four most common birth defects. In
light of the finding that amniocentesis itself carries a 0.5 to
1.5 percent chance of terminating a pregnancy (Robin J.R. Blatt,
Prenatal Tests), the researchers have concluded that "many women
may choose not to have an amniocentesis when informed that the
risk of pregnancy loss is substantially greater than the
likelihood of finding an anomaly". (New England Journal of
Medicine 323, No. 9, Aug 30, 1990)