FIRST TRIMESTER SCREEN

First trimester screening is a noninvasive pregnancy evaluation, performed at 11-13 weeks from the first day of the last period, that can identify more than 85% of babies with Down syndrome and trisomy 18 . The screening involves a combination of ultrasonographic measurement of nuchal translucency (NT) and biochemical analysis of maternal serum levels of two pregnancy-related proteins:  free beta-hCG (beta-human chorionic gonadotropin) and PAPP-A (Pregnancy Associated Plasma Protein-A). 

 How Is First Trimester Screening Performed?

Genetic counseling and ordering of the studies are coordinated through the Prenatal Diagnostic Center.  Dr. Natalie Blagowidow is certified to perform the nuchal tranlucency ultrasound at GBMC. A finger-stick blood sample for the biochemical assays is performed in conjunction with the genetic counseling and ultrasound.  The blood sample is analyzed by NTD Labs, Inc.  See below for specific information about health insurance coverage.

Who Is Eligible For First Trimester Screening?

First trimester screening is designed to detect chromosomal abnormalities in low-risk pregnancies in younger mothers.  Women older than 34 as well as couples with additional risk factors should consider other diagnostic testing procedures, such as amniocentesis or chorionic villus sampling (CVS).

How Accurate Is First Trimester Screening?

Studies have shown that more than 85% of babies with Down syndrome and trisomy 18 will have a positive test result.  Up to 15% of Down syndrome and trisomy 18 cases will not be detected.  Babies with other chromosome disorders or birth defects may not be detected by first trimester screening.

What Do Positive And Negative Results Mean?

A positive test result indicates an increased risk for Down syndrome or trisomy 18 above the accepted baseline cut-off values. The Down syndrome risk used is that of a 35 year old at the same gestational age (1/240-1/260). A positive result for trisomy 18 is indicated by a risk of 1/150 (0.67%) or greater.  For example, a result of 1/50 (2.0%) is considered positive, while a risk of 1/400 (0.25%) is negative.  A positive result is not diagnostic!  It indicates that an increased risk for a problem exists and that additional testing should be considered.  Similarly, a negative result does not totally rule out these abnormalities, but instead decreases the specific risks for Down syndrome and trisomy 18 in

If a positive test result is obtained, the genetic counselor will explain the results and review options for further testing, which may include CVS or amniocentesis and high-resolution ultrasound.  If the results of the screening are within the normal range, maternal serum AFP screening for neural tube defects is recommended at 16 weeks. A detailed ultrasound to screen for neural tube defects and other birth defects is recommended at 18-20 weeks of pregnancy.  Women over age 34 or those with additional risk factors may still opt to have a diagnostic procedure to test for other abnormalities.  

Health Insurance Coverage

The cost  of screening includes genetic counseling, ultrasound, and a lab fee for the biochemical analysis and interpretation.  We suggest that prospective patients call their insurance carriers and provide the following procedure codes (also known as CPT codes) to verify coverage for the first trimester screen.  Most insurance companies require use of a specific laboratory and radiology center, and may not cover services provided by GBMC or NTD Labs.  Only the insurance carrier can tell a patient whether these are covered services and contracted service sites under her policy.  Authorization by a patient's insurance company is not a guarantee of payment.

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