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Home : Specialty Care : Center for Perinatal Care : First Trimester Screening

First Trimester Screening

The First Trimester Screen is an optional, noninvasive prenatal screening test.  It estimates the chances that a woman might have a baby with one of three different genetic conditions: Down syndrome (also called trisomy 21), trisomy 18 and trisomy 13.  Everyone has a background risk to have a baby with one of these conditions and that risk is based on a woman’s age.  The First Trimester Screen however provides a woman with a personalized risk estimate. It is important to understand that this test can not determine for certain if a pregnancy/baby has one of these genetic conditions. 

Who might consider the First Trimester Screen? What are the benefits of the First Trimester Screen?

The First Trimester Screen is commonly offered to all pregnant women, regardless of age.  There are a variety of reasons why someone might consider this test.  Ultimately, it is a woman’s or a couple’s choice to pursue this test. Some benefits include:

  • Determining if there is a higher chance of having a baby with Down syndrome, trisomy 18 or trisomy 13.
  • Using the personalized risk estimate to help a woman decide if she wants to pursue further diagnostic testing such as Chorionic Villus Sampling (CVS) or amniocentesis.
  • Providing information about risk for these genetic conditions earlier than the Quad Screen.
  • Detecting other types of health concerns such as heart defects or other birth defects.

When is the First Trimester Screen performed?

The First Trimester Screen is typically performed between 11 4/7 and 13 6/7 weeks gestation.

What happens during the First Trimester Screen?

The test involves a combination of a special ultrasound examination and a blood test.

First, the patient meets with a genetic counselor before the ultrasound to briefly review the benefits, limitations and risks of the First Trimester Screen. The genetic counselor then takes a small amount of blood from the woman’s finger tip and places it onto a special filter paper.   The blood sample is sent to a laboratory where the levels of two proteins are measured.  These proteins are normally found in a woman’s blood during pregnancy. A woman who is pregnant with a baby with one of these genetic conditions tends to have abnormal levels of these proteins in her blood. 

Next, the woman has an ultrasound, which is performed through the abdomen.  A sonographer, certified by the Fetal Medicine Foundation, examines the baby and checks:   

  • The nuchal translucency (NT).  This is a pocket of fluid found at the back of the baby’s neck.  All babies have this pocket of fluid at the back of the neck, but babies with certain genetic conditions often have a larger than normal pocket of fluid.
  • The nasal bone.  At this stage in pregnancy most babies have a well developed nasal bone that is easy to see by ultrasound.  Babies with Down syndrome, however, tend to have a less developed nasal bone, which in turn is not as well seen by ultrasound and looks absent.

The ultrasound measurement of the NT, presence or absence of the nasal bone and the levels of the proteins are used together to estimate the chance that the baby has Down syndrome, trisomy 18 or trisomy 13.
 
The total time for this appointment is usually around 75 minutes. 

How long do results take? How are the results reported?

The final result, which combines the blood work and ultrasound measurements, is usually available 7 days after the complete test is performed. Results are reported as an “increased risk” (risk higher than the cut-off) or “within the normal range” (risk lower than the cut-off). The cut-off for Down syndrome represents the risk for a woman who is 35 years old. If the results are in the normal range, the patient will receive a letter in the mail. If the results show an increased risk, a genetic counselor will contact the patient by phone to discuss the results of the screen and options for further testing. A copy of the result is sent to the patient’s doctor or midwife.

What is Instant Risk Assessment? Can this test be completed earlier in the pregnancy?

Instant Risk Assessment is way for a woman to receive the final results of the First Trimester Screen the same day as her ultrasound appointment. The blood collection can be completed as early as the 9th week of pregnancy at The Center for Perinatal Care. She then returns to The Center for Perinatal Care between the 11th and 14th week of pregnancy for the ultrasound measurements. Immediately after her ultrasound, a genetic counselor will inform her of her combined final results.  Although this requires the woman to come to the clinic for two appointments, some women prefer this option so that they can get results sooner.

What if the results show that the risk is within the normal range?

When the results are in the normal range it means that the chance of having a baby with Down syndrome, trisomy 18 and/or trisomy 13 is less than the screening cut-off. First trimester screening can never eliminate the chance of having a baby with Down syndrome, trisomy 18, trisomy 13 or other health conditions. Many people feel reassured by a result that is in the normal range, and they may decide not to have a diagnostic test like a CVS or amniocentesis. Other people may wish to have a more definitive diagnosis and they may choose to have a diagnostic test.

What if the results show that the risk is increased or abnormal?

A test result that shows an increased risk means that the risk for Down syndrome or trisomy 13 or trisomy 18 is higher then the screening cut-off. It does not mean that this genetic condition has been diagnosed. In many cases, the baby does not have Down syndrome or trisomy 18 or trisomy 13. A genetic counselor will contact you to discuss the results of the screen. If your first trimester screen results show an increased risk, diagnostic testing is available by either chorionic villus sampling (CVS) until 14 weeks, or amniocentesis starting after 16 weeks. The genetic counselor can discuss these options with you in greater detail.

What is the accuracy of the First Trimester Screen?

First trimester can detect about 91-95% of babies with Down syndrome, Trisomy 18 and Trisomy 13.

What are the limitations of the First Trimester Screen?

  • The First Trimester Screen does not diagnose or tell for certain if a baby does or does not have Down syndrome, trisomy 18 or trisomy 13.
  • The First Trimester Screen does not screen for spina bifida.  A blood test, called the Alpha Fetal Protein (AFP) test, is offered later in the pregnancy to screen for spina bifida.
  • The First Trimester Screen does not screen for all types of genetic conditions, birth defects, or other health problems.  

Can all birth defects be detected by First Trimester Screening or any other screening?

No. No prenatal test can guarantee a child free of birth defects, health problems or learning problems.

What are the risks of the First Trimester Screen?

Besides the discomfort of poking the finger to collect a blood sample, there are no known physical risks to the mother or baby. There is no risk of miscarriage with the First Trimester Screen.  Since this is a screening test, there is a risk of a false positive test result. A false positive test result occurs when the risk estimate shows a “high risk” for having a baby with one of these genetic conditions but after further testing the baby really does not have this diagnosis. A test result that shows an increased risk (i.e. an abnormal First Trimester Screen result) may provoke anxiety.

Are there any special preparations or post-procedure precautions for the First Trimester Screen?

No.  There are no dietary restrictions, you do not need a full bladder, and there are no post-procedure precautions. This test does not require an overnight stay in the hospital.

How long does the test take?

In general, we schedule 75 minutes for the total First Trimester Screen appointment, however this time can vary.  You will first meet with a genetic counselor to review the test process and obtain a blood sample. Next you will have your ultrasound to obtain the nuchal translucency measurement. The blood sample and measurement will be sent to the lab and the combined results are available in about 7 days.  

Where is the First Trimester Screen performed?

This test is completed at The Center for Perinatal Care in Meriter Hospital. Valet parking or parking within Meriter’s parking ramp is available free of charge to our patients.

Does insurance cover the First Trimester Screen?

It is recommended that you check with your insurance company to verify coverage.

Questions?

If you have additional questions, please feel free to contact The Center for Perinatal Care at (608) 417-6667.