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 offer all pregnant women in California the option to be screened for certain birth defects during pregnancy.  You can choose whether or not you want prenatal screening during your 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.
 
Blood Test 1First trimester blood test (10 to 13 weeks):  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 between 10 weeks and 13 weeks 6 days in pregnancy.   

Ultrasound smallNuchal translucency ultrasound (11 to 14 weeks):  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 an area on the fetal neck called the "nuchal translucency" (NT). The NT ultrasound lets the program calculate an initial (preliminary) result for Down syndrome and trisomy 18 and provides early screening for some physical birth defects.

Blood Test 2Second trimester blood test (15 to 20 weeks): 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 found in the blood sample 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 one fetus or more (twins, triplets)
  • Whether you have smoked one or more cigarettes in the week prior to having either blood test

SCREENING RESULTS

When are results available?
Sequential Integrated Screening will give you results at two separate times. The first (preliminary) result is available soon after you have both the first trimester blood test and the NT ultrasound. The second (final) result is available one to two weeks after the second blood test.

Preliminary Result (available before 15 weeks in pregnancy)
The preliminary result provides an early estimate of your risk 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 based on information from both of your blood tests, the measurements from the NT ultrasound, and your age. This information is combined (integrated) to give 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.

What type of result is reported?
Results are reported as either Negative (low risk) or Positive (high risk). Kaiser members with screen positive results are eligible for genetic counseling and follow-up services at 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 their website: Prenatal Screening Program

Last reviewed: December 7, 2017
Reviewed by: Kimberly Barr, MS, LCGC