Determining the viability of a pregnancy is a major challenge, especially with a pregnancy of unknown location. The latest review in our Current Concepts series provides specific guidance, including stringent criteria for nonviability, that can reduce the risk of inadvertent harm to a potentially normal pregnancy. See the video: Ultrasonographic Finding Suspicious for Pregnancy Failure
In diagnosing nonviability of an early pregnancy, a false positive diagnosis — erroneously diagnosing nonviability — carries much worse consequences than a false negative diagnosis — failing to diagnose a nonviable pregnancy.
• What is the typical sequence of events in early pregnancy, as seen on transvaginal ultrasonography?
The gestational sac is first seen at approximately 5 weeks of gestational age, appearing as a small cystic-fluid collection with rounded edges and no visible contents, located in the central echogenic portion of the uterus (i.e., within the decidua). The yolk sac, a circular structure about 3 to 5 mm in diameter, makes its appearance at about 5 1/2 weeks of gestation. The embryo is first seen adjacent to the yolk sac around 6 weeks, at which time a heartbeat can be seen as a flickering motion.
• What do recent studies suggest as a revised cutoff for crown-rump length and mean sac diameter in diagnosing failed pregnancy?
Recent studies suggest that it is prudent to use a cutoff of 7 mm (rather than 5 mm) for crown-rump length with no cardiac activity for diagnosing failed pregnancy. This would yield a specificity and positive predictive value of 100% (or as close to 100% as can be determined). Because cardiac activity is usually visible as soon as an embryo is detectable, the finding of no heartbeat with a crown-rump length of less than 7 mm is suggestive, though not diagnostic, of failed pregnancy. In addition, recent studies, in combination, suggest that it is prudent to use a cutoff of 25 mm (rather than 16 mm) for the mean sac diameter with no visible embryo in diagnosing failed pregnancy. This would yield a specificity and positive predictive value of 100% (or as close to 100% as can be determined). When the mean sac diameter is 16 to 24 mm, the lack of an embryo is suggestive, though not diagnostic, of failed pregnancy.
Morning Report Questions
Q: How do hCG levels help in the diagnosis of a pregnancy of unknown location?
A: In a woman with a pregnancy of unknown location whose hCG level is more than 2000 mIU per milliliter, the most likely diagnosis is a nonviable intrauterine pregnancy, occurring approximately twice as often as ectopic pregnancy. Ectopic pregnancy, in turn, occurs approximately 19 times as often as a viable intrauterine pregnancy when the hCG level is 2000 to 3000 mIU per milliliter and the uterus is empty, and 70 times as often as a viable intrauterine pregnancy when the hCG level is more than 3000 mIU per milliliter with an empty uterus. Ectopic pregnancies are associated with highly variable hCG levels, which are often less than 1000 mIU per milliliter, and the hCG level does not predict the likelihood of a ruptured ectopic pregnancy. That is, a single hCG value, even if low, does not rule out a potentially life-threatening ruptured ectopic pregnancy. Hence, ultrasonography is indicated in any woman with a positive pregnancy test who has clinical signs of an ectopic pregnancy.
Q: Why do the authors consider presumptive treatment for ectopic pregnancy in a hemodynamically stable woman inappropriate?
A: According to the authors, there are a number of reasons why presumptive treatment for ectopic pregnancy with the use of methotrexate or other pharmacologic or surgical means is inappropriate if the woman is hemodynamically stable. First, there is a chance of harming a viable intrauterine pregnancy, especially if the hCG level is 2000 to 3000 mIU per milliliter. Second, the most likely diagnosis is nonviable intrauterine pregnancy (i.e., failed pregnancy), and methotrexate is not an appropriate treatment for a woman with this diagnosis. Third, there is limited risk in taking a few extra days to make a definitive diagnosis in a woman with a pregnancy of unknown location who has no signs or symptoms of rupture and no ultrasonographic evidence of ectopic pregnancy. Fourth, the progression of hCG values over a period of 48 hours provides valuable information for diagnostic and therapeutic decision-making. Thus, it is generally appropriate to do additional testing before undertaking treatment for ectopic pregnancy in a hemodynamically stable patient.