Genetics Northern California

Sequential Integrated Screening

Sequential 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 does not look for all types of birth defects.

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

Sequential Integrated Screening has three separate steps: two blood tests and one ultrasound.
 
First trimester blood test:  Sequential Integrated Screening starts with a first trimester blood test that measures two substances in your blood:  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.
 
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.   
 
Nuchal translucency ultrasound:  The second step for Sequential Integrated Screening is a special ultrasound done from 11 weeks 2 days to 14 weeks 2 days of the pregnancy. This ultrasound measures the size of the "nuchal translucency" (NT) of the fetus. Including an NT measurement in the screening test improves the detection of Down syndrome and trisomy 18 compared to either Serum Integrated screening or Quad Marker screening. This ultrasound can also provide early detection of some physical birth defects.
 
Second trimester blood test: The final step of Sequential 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).
 
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

Sequential Integrated Screening Test Results
You will most likely get a "SCREEN NEGATIVE" result from your screening test.  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. Instead this result estimates 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.  
  
A small number of women will get a "SCREEN POSITIVE" result.  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 amounts 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.

Preliminary Result  (First trimester result)  
Sequential Integrated Screening provides an early estimate of your risk for Down syndrome and trisomy 18, called a preliminary result. Once you have completed both the first trimester blood test and the NT ultrasound, a first trimester risk estimate will be calculated. The preliminary result only has information about the risks for Down syndrome and trisomy 18. If the chance for both of these conditions is lower than the State's cut-offs, your preliminary result is considered screen negative. A final result cannot be calculated until you have your second trimester blood test. When you have the second trimester blood test your final result includes a refined risk for Down syndrome and trisomy 18 as well as risks for the other conditions, such as spina bifida.  
 
If your preliminary result is screen positive, a genetic counselor will talk with you about your result. You are offered the option of having a diagnostic test, either CVS or amniocentesis; or you can choose to complete Sequential Integrated Screening before making a decision about diagnostic testing. If you choose Sequential Integrated Screening, you will get your final result after the second trimester blood test.
 
Final Result 
Your final result is calculated based on the information from both of your blood tests, the measurements from the NT ultrasound, and your age. This information is combined (integrated) to provide you with the best risk estimate for each birth defect included in the screening test. If all of the risks are lower than the State's cut-offs, your result is considered "Screen Negative". If any of the estimated risks are higher than the State's cut-offs, your result is considered screen positive, and follow-up services are offered, including genetic counseling, detailed ultrasound, and amniocentesis.

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