A prenatal ultrasonic measurement of the thickness or translucent area below the SKIN in the back of the fetal NECK, or nape of the neck, during the first 11-14 weeks of gestation (PREGNANCY TRIMESTER, FIRST). Abnormal thickness or nuchal translucent measurements resulting from fluid collection, is associated with increased risks of CHROMOSOME ABNORMALITIES. (Nicolaides et al., 1992).