 Control subjects are recruited from the Prenatal Diagnostic Clinic at UNC-Chapel Hill, which performs over 12,000 prenatal ultrasound scans a year. Please note that all pregnant women in North Carolina are referred for an ultrasound at gestational age 18 weeks as part of routine prenatal care. Subjects with Turner syndrome are identified through the UNC Turner Syndrome clinic, through advertisements with relevant local and national support groups such as the Turner Syndrome Society, and through genetic counselors and other relevant health professionals throughout the United States. 