First trimester screening includes an ultrasound exam to measure the size of the clear space in the tissue at the back of a baby's neck (nuchal translucency). In Down syndrome, the nuchal translucency measurement is abnormally large — as shown on the left in the ultrasound image of an 11-week fetus. For comparison, the ultrasound image on the right shows an 11-week fetus with a normal nuchal translucency measurement.
Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission.
Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press.
Your GivingTuesday gift can go 2X as far.