Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester

T h e n e w e ngl a nd j o u r na l o f m e dic i n epregnancies. 10,35 In addition, the inter observervariation in the measurement of the mean sacdiameter is ±19%, 32 so a diameter of 21 mm (theupper limit above) as measured by one observermay be 19% greater, or 25 mm, when measuredby another observer.These studies, in combination, suggest that itis prudent to use a cutoff of 25 mm (rather than16 mm) for the mean sac diameter with no visibleembryo (Table 2) in diagnosing failed pregnancy(Fig. 2B and 2C). This would yield a specificityand positive predictive value of 100% (or as closeto 100% as can be determined). When the meansac diameter is 16 to 24 mm, the lack of an embryois suspicious for, though not diagnostic of,failed pregnancy (Fig. S2 in the SupplementaryAppendix).Time-based Criteria for Failed PregnancyNot all failed pregnancies ever develop a 7-mmembryo or a 25-mm gestational sac, so it is importantto have other criteria for diagnosingpregnancy failure. The most useful of such criteriainvolve nonvisualization of an embryo by acertain point in time. An alternative approach topredicting pregnancy failure, based on subnormalgrowth of the gestational sac and embryo,has been shown to be unreliable. 36Nonvisualization of an embryo with a heartbeatby 6 weeks after the last menstrual periodis suspicious for failed pregnancy, but dating ofthe last menstrual period (in a pregnancy conceivedwithout medical assistance) is too unreliablefor definitive diagnosis of pregnancy failure.37 The timing of events in early pregnancy— gestational sac at 5 weeks, yolk sac at 5 1 ∕2weeks, and embryo with heartbeat at 6 weeks— is accurate and reproducible, with a variationof about ± 1 ∕2 week 14,15 ; this consistency explainsthe time-related criteria for pregnancy failurelisted in Table 2. For example, if the initial ultrasonogramshows a gestational sac with a yolk sacand a follow-up scan obtained at least 11 dayslater does not show an embryo with cardiac activity,the diagnosis of failed pregnancy is established(Fig. 2D and 2E; also see Fig. S3 in theSupplementary Appendix).Other Suspicious FindingsSeveral ultrasonographic findings early in thefirst trimester have been reported as abnormal.These include an “empty” amnion, 38 an enlargedyolk sac, 39 and a small gestational sac. 40 Criteriafor these abnormal findings are presented inTable 2. Because none of these signs have beenextensively studied, they are considered to besuspicious for, though not diagnostic of, failedpregnancy.Di agnosing a nd Ruling Ou ta V iable Intr auter ine Pr egnancyin a Woman with a Pregnancyof Unknown LocationThe evaluation and management of a pregnancyof unknown location have received considerableattention, with various flow charts and mathematicalmodels proposed for use in this context.41,42 Our intent here is not to review thebroad topic of pregnancy of unknown location,but instead to focus on one important element:the role of an hCG level at a single point in timein diagnosing or ruling out a viable intrauterinepregnancy and in guiding patient-care decisions.The hCG levels in viable intrauterine pregnancies,nonviable intrauterine pregnancies, andectopic pregnancies have considerable overlap,so a single hCG measurement does not distinguishreliably among them. 2,4,43 Considerableresearch during the past 30 years has sought todetermine the discriminatory hCG level: thevalue above which an intrauterine gestationalsac is consistently seen on ultra sonography innormal pregnancies. An early study, based ontransabdominal ultrasonography, put the level at6500 mIU per milliliter. 44 With improvements inultrasonographic technology, including the introductionof transvaginal ultrasonography, gestationalsacs became detectable earlier in pregnancy,and the reported discriminatory hCGlevel was brought down to 1000 to 2000 mIU permilliliter. 45-47 As with the crown–rump lengthand mean sac diameter, however, more recentresearch has shown that previously acceptedvalues for the discriminatory hCG level are notas reliable for ruling out a viable pregnancy asoriginally thought.One reason for the lower reliability of thediscriminatory hCG level today than was reportedin the past may be the fact that multiplegestations, which are associated with higherhCG levels at a given stage of pregnancy thanare singleton gestations, are more commonnow than they were 20 to 30 years ago. Failureof the discriminatory hCG level to rule out aviable intrauterine pregnancy, however, has1448n engl j med 369;15 nejm.org october 10, 2013The New England Journal of MedicineDownloaded from nejm.org on October 10, 2013. For personal use only. No other uses without permission.Copyright © 2013 Massachusetts Medical Society. All rights reserved.