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
A screen negative result means that the chance for Down syndrome, neural tube defects, abdominal wall defects, trisomy 18, and SLOS is low enough that follow-up testing is not routinely offered. Up to 95% of women will have a screen negative result. It is important to remember that a screening test will not tell for certain whether the baby actually has a birth defect, but instead tells the chance of a specific problem occurring. Some women whose babies actually have one of the birth defects included in the California Prenatal Screening Program will be missed with the screening test.

Screen Positive Result
A screen positive result means that there is a higher chance for certain birth defects in your pregnancy, such as Down syndrome, neural tube defects, abdominal wall defects, trisomy 18 or SLOS. Most of the time, however, the reason for the screen positive result is NOT a birth defect. The most common reason for this type of result is normal variation. In other words, the amounts of the substances are different than average, but normal for your baby.

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