The Alpha-fetoprotein (AFP) Screen is a second trimester screen that assesses the risk of a baby being born with open neural tube defects (ONTDs) by measuring solely the level of alpha-fetoprotein in maternal serum. This screen is performed between 15 weeks to 22 weeks, 6 days of gestation.
In pregnancies affected by ONTDs, such as open spina bifida or anencephaly, the level of AFP tends to be elevated.
What Does a Negative Result Mean?
The result is considered screen negative if the risk for ONTDs are lower than the cutoff used. Typically, a cutoff of one in 104 is used for ONTDs. Although a screen negative result indicates a reduction in a patient’s risk of having a baby with ONTDs, a screen negative result does not completely rule out the possibility of a pregnancy with this condition.
What Does a Positive Result Mean?
A screen positive result for ONTDs by the AFP Screen means that the patient has a risk to have a baby with an ONTD of greater than or equal to one in 104.
What is the Detection Rate for ONTDs?
The AFP Screen will detect about 85% of singleton pregnancies affected with ONTDs.
What Other Tests may be Offered if an AFP Screen is Positive?
Depending on the results of the AFP Screen, additional testing may be offered including a second trimester detailed anatomy ultrasound and prenatal diagnosis (amniocentesis). Genetic counseling is also recommended.