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Early Pregnancy-- NUMBERS to know!! 

Convened by the Society of Radiologists in Ultrasound (SRU)- team led by Dr. Peter Doubilet, PhD, of Brigham and Women's Hospital and Harvard Medical School (NEJM, October 10, 2013, Vol. 369:15, pp. 1443-1451).-- the following is quoted/adapted from http://www.auntminnie.com/index.aspx?sec=ser&sub=def&pag=dis&ItemID=105083

Findings diagnostic of pregnancy failure: 
Crow rump length CRL of ≥ 7 mm and no heartbeat
Mean sac diameter (MGSD) of ≥ 25 mm and no embryo
Absence of embryo with heartbeat ≥ 2 weeks after a scan that showed a gestational sac without a yolk sac 
Absence of embryo with heartbeat ≥ 11 days after a scan that showed a gestational sac with a yolk sac

Findings suspicious for but not diagnostic of pregnancy failure: 
CRL of < 7 mm and no heartbeat
MGSD of 16-24 mm and no embryo
Absence of embryo with heartbeat 7-13 days after a scan that showed a gestational sac without a yolk sac
Absence of embryo with heartbeat 7-10 days after a scan that showed a gestational sac with a yolk sac
Absence of embryo ≥ 6 weeks after last menstrual period (with reliable LMP history!!)
Empty amnion (amnion seen adjacent to yolk sac, with no visible embryo)
Enlarged yolk sac (> 7 mm)
Small gestational sac in relation to the size of the embryo (< 5 mm difference between mean sac diameter and crown-rump length)

Pregnancy of unknown location and use of quantitative bHCG 
The panel also determined diagnostic and management guidelines related to the possibility of a viable intrauterine pregnancy in a woman with a pregnancy of unknown location. 

For the finding of no intrauterine fluid collection and normal (or near-normal) adnexa on ultrasonography, the authors provided the following key points: 

****A single measurement of human chorionic gonadotropin (hCG), regardless of its value, does not reliably distinguish between ectopic and intrauterine pregnancy (viable or nonviable).
***If a single hCG measurement is < 3,000 mIU/mL, presumptive treatment for ectopic pregnancy with the use of methotrexate or other pharmacologic or surgical means should not be undertaken, in order to avoid the risk of interrupting a viable intrauterine pregnancy.
If a single hCG measurement is ≥ 3,000 mIU/mL, a viable intrauterine pregnancy is possible but unlikely. The most likely diagnosis is a nonviable intrauterine pregnancy, so it is generally appropriate to obtain at least one follow-up hCG measurement and followup ultrasonogram before undertaking treatment for ectopic pregnancy.
(note from Dr. Chiowanich: caveats of using high > 3000 HCG are early multiple gestation or recent miscarriage/spontaneous abortion of previously undocumented IUP by ultrasound)

If ultrasound had not yet been performed, the researchers offered the following key point: "The hCG levels in women with ectopic pregnancies are highly variable, often < 1,000 mIU/mL, and the hCG level does not predict the likelihood of ectopic pregnancy rupture," they wrote. "Thus, when the clinical findings are suspicious for ectopic pregnancy, transvaginal ultrasonography is indicated even when the hCG level is low."

Panel member Dr. Kurt Barnhart, an ob/gyn at Perelman School of Medicine at the University of Pennsylvania, said in a statement that the guidelines represent a consensus that will balance the use of ultrasound and the time needed to ensure that an early pregnancy is not falsely diagnosed as nonviable. 

"There should be no rush to diagnose a miscarriage; more time and more information will improve accuracy and hopefully eliminate misdiagnosis," he said in the statement.