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9 weeks

What Will Happen At The First Trimester Screen?

I’m having my First Trimester Screen. What should I expect?

The First Trimester Screen is a new optional test used to look for chromosomal abnormalities such as Down syndrome. The screening involves two parts: a blood test and an ultrasound. If you decide to have a First Trimester Screen, a lab will draw a sample of blood from your arm. The blood sample will be used to measure your levels of two pregnancy hormones, HCG and PAPP-A. Ultrasound is used to measure what’s called nuchal translucency, or the fluid beneath the skin of your baby’s neck. The results of the blood test and ultrasound — along with your age — can help your healthcare provider calculate the odds that your baby has a chromosomal abnormality.

It’s important to understand that the First Trimester Screen is a screening test; it is not diagnostic. So it will just give you the odds that there is a problem, not diagnose one. If your First Trimester Screen suggests that you’re likely carrying a baby with a chromosomal abnormality, your healthcare provider may recommend additional testing, such as an amniocentesis, to confirm or rule out the diagnosis.

Some women opt out of the screening altogether, reasoning that they wouldn’t change anything even if the test suggests that their baby may have an abnormality. Other women choose to go ahead with the screen. The choice is entirely yours, so discuss the risks and benefits of First Trimester Screening with your healthcare provider before making a decision.

Plus, more from The Bump:

Your Guide to Prenatal Tests and Checkups

Are Early Ultrasounds Okay?

First Trimester To Dos

By Sharon Phelan, MD, professor of obstetrics and gynecology at the University of New Mexico - Albuquerque