DeFranco Emily, Gross Gilad, Shanks Anthony, Johnson Traci, Shen Tammy
Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Washington University in St Louis, MO, USA.
Am J Obstet Gynecol. 2008 Sep;199(3):e1-4. doi: 10.1016/j.ajog.2008.07.026.