First Trimester Screening

First Trimester Screening

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 90 percent of babies with Down syndrome, trisomy 18, and trisomy 13. 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.  The physicians and staff are certified to perform the nuchal translucency 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. In some situations, your insurance may be contracted with a lab other than NTD Labs. Having the study performed at a different laboratory may alter the test's detection rate (the ability to identify pregnancies with Down syndrome or other chromosomal abnormalities).

Who Is Eligible For First Trimester Screening?
First trimester screening is designed to detect chromosomal abnormalities in low-risk pregnancies or to provide further risk assessment in pregnancies considered to be at increased risk. For women who prefer a definitive answer regarding a chromosomal condition in the pregnancy, amniocentesis or Chorionic Villus Sampling (CVS) should be considered.

How Accurate Is First Trimester Screening?
Studies have shown that more than 90 percent of babies with Down syndrome, trisomy 18, and trisomy 13 will have a positive test result.  Up to 10 percent 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, trisomy 18 or trisomy 13, 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 percent) or greater.  For example, a result of 1/50 (2.0 percent) is considered positive, while a risk of 1/400 (0.25 percent) 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 rule out these abnormalities, but instead decreases the specific risks for Down syndrome, trisomy 18 or trisomy 13 in the pregnancy.

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. In some instances, a sequential screen is offered. The sequential screen will provide further revision of a woman's Down syndrome risk by combining results of first trimester screening with results of second trimester blood work.  A detailed ultrasound to screen for neural tube defects and other birth defects is recommended at 18-20 weeks of pregnancy.  Women may still opt to have a diagnostic procedure in order to have a definitive diagnosis. The decision to proceed to amniocentesis or CVS is based on many factors, including the risk of fetal chromosomal abnormality, the risk of the procedure, and the consequences of having an affected child if diagnostic testing is not done.

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.

 Procedure  CPT  Code
Genetic Counseling  99213
OB Ultrasound 76813
Blood Testing (NTD Labs)

84704 / 84163


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