First Trimester Screen

First Trimester Screen

First trimester screening can tell you if your baby is at risk for having certain genetic conditions. Sometimes, those genetic conditions can also cause birth defects. First trimester screening may help parents make decisions about further testing.

What is a chromosome condition?

Most commonly, a chromosome condition means a person has an extra chromosome. 

The most common chromosome condition is Down syndrome, caused by an extra copy of chromosome 21 (also called trisomy 21). This extra chromosome causes learning and growth differences, and other possible birth defects. 

An extra chromosome 18 causes the disorder trisomy 18 (also known as Edwards syndrome). This disorder is more severe but less common than Down syndrome.

When is first trimester screening done?

The best time to have a first trimester screening is between 12 weeks 0 days and 13 weeks 6 days of pregnancy.

What does the screening include?

First trimester screening includes an ultrasound and a blood test.

The ultrasound measures a pocket of fluid at the back of your baby’s neck called nuchal transluscency (or NT). The ultrasound can also detect up to 50 percent of major birth defects.

The blood test checks the levels of certain proteins normally present during pregnancy. If protein levels are higher or lower than average, the pattern can determine whether the pregnancy has an increased risk for chromosome conditions. If one protein (PAPP-A) is very low, this can indicate increased risk for preeclampsia or growth issues for the baby later in the pregnancy.

What do the results mean?

Results are reported as low risk or increased risk. The results do not confirm or rule out Down syndrome or trisomy 18. The results only identify babies at a higher risk for one of these conditions.

Low risk
A low-risk result mean that your baby’s risk for a chromosome condition is decreased. A low risk is reassuring but does not completely rule out the possibility of a chromosome condition, such as Down syndrome.

Increased risk 
An increased-risk result means that there is an increased risk for a chromosome condition. 
If results show an increased risk, you will be offered further testing. The decision to have more testing is up to you. 

Other testing

Talk to your clinician about other tests available later in your pregnancy. You can also ask your clinician about genetic counseling. Genetic counselors are a good source for information on different testing options and evaluation. 
 

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