Genetics Northern California

Serum Integrated Screening

Serum Integrated Screening is a voluntary prenatal test available to pregnant women who start prenatal care before the 14th week in pregnancy. This screening test is part of the California Prenatal Screening Program. The goal of the Prenatal Screening Program is to provide an opportunity for all pregnant women in California to have screening for certain birth defects during the pregnancy.  It is important to remember that this test cannot look for all types of birth defects.

Below is a list of the conditions included in the California Prenatal Screening Program:

Serum Integrated Screening is done by two separate blood tests.

First trimester blood test:  Serum Integrated Screening starts with a first trimester blood test that measures two substances in your blood: beta human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein-A (PAPP-A). These substances are normally found in a woman's blood only during pregnancy.  By including the first trimester blood test in the screening test, the detection of Down syndrome and trisomy 18 is improved, compared to using only the second trimester blood test (Quad Marker screening).  The first blood test is done by taking a small amount of blood from your arm from 10 weeks to 13 weeks 6 days in pregnancy.

Second trimester blood test: The second part of Serum Integrated Screening is a blood test done from 15 weeks to 20 weeks in pregnancy. This blood test measures the levels of four substances naturally found in a pregnant woman's blood. These substances are: 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). This is the same blood test as Quad Marker screening.

The amount of each substance in both the first trimester and second trimester blood samples is 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 either blood test  
     

Serum Integrated Screening Test Results

Your final result is calculated based on the information from both of your blood tests and your age. The result is usually available about one to two weeks after the second blood test.  No results are available in the first trimester of pregnancy. The blood test results are combined (integrated) to provide you with a risk estimate for each birth defect included in the screening test. If all of the risks are lower than the State cut-offs, your result is considered "Screen Negative". If any of the estimated risks are higher than the State cut-offs, your result is considered "Screen Positive", and follow-up services are offered, including genetic counseling, detailed ultrasound, and amniocentesis.

Screen Negative:  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 not be picked up by the screening test.

Screen Positive:  A screen positive result means that there is an increased 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 amount of the substances are different than average, but normal for your baby.

The California Prenantal Screening Program provides handouts for all screen positive results: www.cdph.ca.gov/programs/pns/Pages/InformationforPatients

Kaiser members with screen positive results are eligible for genetic counseling and follow-up services at any Kaiser Permanente Genetics Department, or any of the State-approved Prenatal Diagnosis Centers.  There is no additional fee for these follow-up services.

For more information about the California Prenatal Screening Program go to their website: www.cdph.ca.gov/programs/pns 

Last reviewed: January 11, 2013
Reviewed by: Kaiser Permanente Genetics