AbstractJDMS 14:185-186 July/August 1998 185 WHAT'S NEW! * In a presentation at the American Institute of Ultrasound in Medicine's 42nd Annual Convention titled, "The Appearing Twin: Undercounting of Mul- tiple Gestations on Early First Trimester Sonograms," results of a recent study by Peter Doubilet, MD and Carol Benson, MD, of Brigham and Women's Hos- pital and Harvard Medical School in Boston, showed that sonography before 6 weeks of pregnancy dramat- ically undercounts multiple gestations. Before the advent of ultrasound, a pregnant woman had no way of knowing with certainty how many fetuses she was carrying. Unexpected delivery of twins and higher order multiples was not uncom- mon. Ultrasound can help avoid these surprises be- cause one of its important roles is to determine whether a woman is carrying a singleton, twins, trip- lets or more. In Drs. Doubilet and Benson's study, thex found that ultrasound performed earl) in the first trimester may fail to identify twins in a signifi- cant number of women who are carrying two fetuses. They found numerous cases in which a woman had a sonogram early in pregnancy demonstrating a single- ton, followed by a second sonogram a few weeks later unexpectedly showing twins.