Evaluation of a New Model for Human Chorionic Gonadotropin Rise in Pregnancies of Unknown Viability

Department of Obstetrics and Gynecology, Women & Infants Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island Department of Maternal Fetal Medicine, Women & Infants Hospital of Rhode Island, Warren Alpert Medical School of Brown University, Providence, Rhode Island Guidelines for Letters. Letters posing a question or challenge to an article appearing in Obstetrics & Gynecology should be submitted within 8 weeks of the article’s publication online. Letters received after 8 weeks will rarely be considered. Letters should not exceed 350 words, including signatures and 5 references. Letters will be published at the discretion of the Editor. The Editor may send the letter to the authors of the original paper so their comments may be published simultaneously. The Editor reserves the right to edit and shorten letters. Letters should be submitted using the Obstetrics & Gynecology online submission and review system, Editorial Manager (http://ong.edmgr.com). Financial Disclosure The authors did not report any potential conflicts of interest.