Doubling time of human chorionic gonadotropin (hCG) in early normal pregnancy: relationship to hCG concentration and gestational age**Presented in part at the Thirty-Third Annual Meeting of the Society for Gynecologic Investigation, March 19 to 22, 1986, Toronto, Ontario, Canada.††The opinions expressed in this article are those of the authors and not necessarily those of the United States Air Force or the Department of Defense.