A woman with pain or bleeding in early pregnancy may have a viable intrauterine, a failing intrauterine, or an ectopic pregnancy. Serum human chorionic gonadotropin (hCG) measurement and pelvic ultrasonography are used to distinguish between an intrauterine pregnancy of uncertain viability and a pregnancy of unknown location.
A false-positive diagnosis of nonviability may lead to interventions that terminate or severely damage a viable pregnancy, whereas a false-negative diagnosis will typically lead only to a short delay in intervention for a failed pregnancy. For a pregnancy of unknown location, harming a potentially normal intrauterine pregnancy is much worse than the results of a false-negative diagnosis, which would involve a short delay in treatment of an ectopic pregnancy in a woman without an adnexal mass. Criteria for diagnosing nonviability in early pregnancy should virtually eliminate false-positive results, that is, have a specificity of ~100%, which yields a positive predictive value (PPV) of 100% for nonviability.
The criteria used to diagnose pregnancy failure in an intrauterine pregnancy of uncertain viability are the absence of cardiac activity by the time the embryo has reached a certain crown-rump length, absence of a visible embryo when the gestational sac has reached a certain size (mean sac diameter), and absence of a visible embryo by a specific time point. Recent studies suggest using a cutoff of 7 mm for crown-rump length with no cardiac activity for diagnosing failed pregnancy. This would yield a specificity and PPV of nearly 100%. The finding of no heartbeat with a crown-rump length of less than 7 mm is suggestive of, but not diagnostic of, failed pregnancy. The mean sac diameter increases as pregnancy progresses. A cutoff of 25 mm should be used with no visible embryo. This would yield a specificity and PPV of close to 100%. When the mean sac diameter is 16 to 24 mm, lack of an embryo is suggestive of, but not diagnostic of, failed pregnancy. Because not all failed pregnancies develop a 7-mm embryo or a 25-mm gestational sac, other criteria are necessary, the most useful of which involve nonvisualization of an embryo by a certain time. Early sonographic pregnancy dating includes a gestational sac at 5 weeks, yolk sac at 5½ weeks, and an embryo with a heartbeat at 6 weeks. Other suspicious findings include an “empty” amnion, an enlarged yolk sac, and a small gestational sac, all of which are considered as suggestive of, but not diagnostic of, failed pregnancy.
The hCG levels in viable intrauterine, nonviable intrauterine, and ectopic pregnancies overlap considerably. Therefore, a single hCG measurement does not distinguish among them. If the hCG level is 2000 to 3000 mIU/mL, a viable intrauterine pregnancy is possible and could be harmed if the woman is treated for an ectopic pregnancy. The progression of hCG values over 48 hours is often used for making diagnostic and therapeutic decisions. But women with ectopic pregnancies have highly variable hCG levels, often less than 1000 mIU/mL, and the hCG level does not predict the likelihood of rupture. Ultrasonography is indicated in any woman with a positive pregnancy test who is clinically suspected of having an ectopic pregnancy.
Stricter criteria for the diagnosis of nonviability are needed to minimize or avoid false-positive test results. If more current and appropriate guidelines are available for practitioners who diagnose and manage problems in early pregnancy, patient care could be improved, and the risk of inadvertent harm to potentially normal pregnancies could be reduced.
Brigham and Women’s Hospital and Harvard Medical School, Boston, MA; Queen Charlotte’s and Chelsea Hospital, Imperial College, London, UK; and University of South Carolina, Columbia, SC