Genetics Northern California

Serum Integrated Screening

Serum Integrated Screening is a test offered to all pregnant women in California who are less than 14 weeks pregnant when they start prenatal care. This is part of the California Prenatal Screening Program and is done to help detect birth defects during pregnancy. You can choose whether or not you want a prenatal test to look for birth defects. 

What does this test look for?  
How is this test done? 
When are the results available?
What type of result is reported?  

What does this test look for? 
This test does not look for all types of birth defects. This test looks for the following conditions:

How is this test done? 
This test is done by taking a small amount of blood from your arm at two different times during pregnancy.  

Blood Test 1First trimester blood test (10 to 13 weeks): Testing starts with one blood sample taken between 10 weeks and 13 weeks 6 days in pregnancy. This part of the test measures two substances in your blood: human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein-A (PAPP-A). These are normally found in a woman's blood only during pregnancy.  

Blood Test 2Second trimester blood test (15 to 20 weeks): The second part of the test is done by taking another blood sample between 15 weeks to 20 weeks in pregnancy. This measures four substances found in a pregnant woman's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin-A (INH) These substances are made by the placenta and the fetus (developing baby).  

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 or not you have diabetes
  • How many babies you are carrying 
  • Whether or not you smoked cigarettes the week before having either blood test

When are the results available?
Both blood tests must be done before any result is reported. Results are ready about one to two weeks after the second blood test. 

What type of result is reported?  
This screening test estimates your risk for each of the selected birth defects. Results are reported as either "negative" (low risk) or "positive" (high risk). Women with positive results are offered genetic counseling and follow-up services. Follow-up can be arranged through any

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.

For more information about the California Prenatal Screening Program go to: Prenatal Screening Program

Last reviewed: April 14, 2020
Reviewed by: Kimberly Barr, LCGC - Kaiser Permanente Genetics