What is First-Trimester Screen?

Optional non-invasive evaluation that combines a maternal blood screening test with an ultrasound evaluation of the fetus.

What is use of First-Trimester Screen?

It will identify risk for specific chromosomal abnormalities, including Down Syndrome Trisomy-21 and Trisomy-18. 

Can it identify other fetal abnormalities?

It can assist in identifying other significant fetal abnormalities, such as cardiac disorders.   

Can it detect neural tube defects?


It does not detect neural tube defects. 

What is COMBINED ACCURACY RATE for the screen to detect the chromosomal abnormalities?

COMBINED ACCURACY RATE - Approximately 85% 


What is meaning of COMBINED ACCURACY RATE approximately 85?

Approximately 85 out of every 100 babies affected by the abnormalities addressed by the screen will be identified.

What is meaning of FALSE POSITIVE RATE of 5%?

Approximately 5% of all normal pregnancies will receive a positive result or an abnormal level.

Parents should be aware of the possibility of receiving abnormal results and then finding, after further testing, the baby is normal. 

What is meaning of POSITIVE TEST?

  1. POSITIVE TEST means you have a 1/100 to 1/300 chance of experiencing one of the abnormalities.
  2. POSITIVE RESULT does not equate to having an abnormality
  3. POSITIVE TEST serves as a prompt to discuss further testing. 

What is a screening test?

Screening tests do not look only at results from the blood test.  

They compare a number of different factors (including age, ethnicity, results from blood tests, etc.) and then estimate what a person’s chances are of having an abnormality.


How is the First-Trimester Screen performed?

How much time it takes?

The blood screen involves drawing blood from the mother, which takes about 5 to 10 minutes. 

The blood sample is then sent to the laboratory for testing. 

The ultrasound is performed by an ultrasound specialist and takes between 20 and 40 minutes. 

The results are evaluated within a week of the testing. 

What are the risks and side effects to the mother or baby?

NO known risks or side effects 

When is the First-Trimester Screen performed?

Between the 11th and 13th week of pregnancy 

What is advantage of First-Trimester Screen?

Mother can consider undergoing an early (first-trimester) diagnostic test, 

such as chorionic villus sampling, or second-trimester amniocentesis. 

What does the First-Trimester Screen look for?


2.   hCG

3.   PAPP-A


By combining above results it determines an overall risk factor for chromosomal abnormalities. 

What is a normal nuchal translucency measurement at 12 weeks?

At 12 weeks of gestational age, an"average" nuchal thickness of 2.18 mm has been observed; 

however, up to 13% of chromosomally normal fetuses present with a nuchal translucency of greater than 2.5 mm. 

What is abnormal nuchal translucency?

The risk is proportional to the nuchal translucency thickness, 

in fact it statistically increases after measurement reaching 3.5 mm or more. 

When nuchal translucency should be measured?

Between 11 and 14 weeks' gestation  

Can increased nuchal translucency be normal?

About 5% of fetuses with a normal karyotype will have an increased NT (5% false positive rate). 

What do the First-Trimester Screen results mean?

You will be told whether your results are “normal or abnormal”, 

and you will be given a risk level by your genetic counselor.

Abnormal test results warrant additional testing for making a diagnosis.