Genetics Northern California

AFP4 (Quad Marker) Screening

AFP4 (Quad Marker) screening is an optional blood test done between 15 weeks to 21 weeks in pregnancy.  This test may be offered when cell-free DNA screening cannot be done. The test looks for certain birth defects during pregnancy. The choice to have this test is up to you. 

Below is a list of the conditions AFP4 can help detect:

AFP4 measures four substances found in your blood when you are pregnant: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin-A (INH). These are made by the placenta and the developing baby. The chance for birth defects is estimated based on your blood test values and your age.

The amount of each substance can be affected by many factors including:

  • Your gestational age (how far along you are in the pregnancy)
  • Your weight
  • Your race (ethnicity or ancestry)
  • Whether you have diabetes
  • Whether you have a single fetus or twins
  • Whether you have smoked one or more cigarettes in the week prior to having your blood test.  

AFP4 Test Results

Your result is available about one to two weeks after your blood is drawn. 

Most results are "Screen Negative". This means the chance is low for the baby to have any of the birth defects the test looks for and no follow-up is needed. 

When the result is "Screen Positive", the chance for a birth defect is high enough to offer follow-up services. This could include genetic counseling, detailed ultrasound, and amniocentesis. 

Screen Negative Result
Most people get screen negative results. A screen negative result means that the chance for Down syndrome, trisomy 18, neural tube defects, and abdominal wall defects is low enough that follow-up testing is not routinely offered.  This result does not guarantee there are no birth defects or genetic conditions. This test can sometimes miss one of the conditions on the screening test (false negative result).

Screen Positive Result
A screen positive result means there is a difference in the expected amount of one or more of the substances being tested. This could be due to one of the conditions the test looks for: Down syndrome, trisomy 18, or a birth defect of the spine or belly. The chance is high enough that more testing will be offered. However, this result does not always mean there is a problem with the baby or the pregnancy. Most pregnancies with positive results are normal.

Last reviewed: September 21, 2022
Reviewed by: Kimberly Barr, MS, LCGC