SAN FRANCISCO – Beta-HCG values can vary widely in early pregnancy, and should not be used in isolation to declare a pregnancy to be abnormal, according to Dr. Jody Steinauer.
In 366 women with vaginal bleeding or pain who went on to have a normal intrauterine pregnancy, the lowest level of beta-HCG at which an intrauterine pregnancy could be seen was 390 mIU/mL. The same study reported that women with beta-HCG levels as high as 3,510 mIU/mL in whom no gestational sac can be seen may still have normal pregnancies (Obstet. Gynecol. 2013;121:65-70).
The widely accepted upper cutoff value is 1,500-2,000 mIU/mL, Dr. Steinauer said at a conference on women’s health sponsored by the University of California, San Francisco. Yet "it’s not a hard-and-fast rule. We have all heard of patients who had even higher beta-HCG levels and went on to have normal singleton pregnancies." On the lower end of beta-HCG values, the attitude may be "her beta-HCG is only 700 mIU/mL, so I’m not expecting to see a gestational sac" on ultrasound. Dr. Steinauer said.
In the current study, using a beta-HCG cutoff of 1,500 mIU/mL when no gestational sac can be seen would identify 80% of normal intrauterine pregnancies. A 2,000-mIU/mL cutoff would identify 91% of normal pregnancies. With either cutoff value, "there would have been a high proportion of normal pregnancies that were called abnormal," said Dr. Steinauer of the university.
New criteria released by the Society of Radiologists in Ultrasound for diagnosing a nonviable pregnancy early in the first trimester also address beta-HCG levels. If no gestational sac is visible at a beta-HCG level greater than 2,000 mIU/mL, an ectopic pregnancy is 19 times more likely than a viable pregnancy, but a nonviable intrauterine pregnancy still is twice as likely as an ectopic pregnancy (N. Engl. J. Med. 2013;369:1443-51).
Those estimates apply to the general U.S. population, Dr. Steinauer said, and may vary depending on patient population.
In women with beta-HCG levels of 2,000-3,000 mIU/mL, there will be 19 ectopic pregnancies and 38 nonviable pregnancies for every viable pregnancy. Yet as many as 2% of women with values this high can have viable pregnancies, according to the society’s criteria. Once the beta-HCG level climbs higher than 3,000 mIU/mL and no gestational sac is visible, an ectopic pregnancy is 70 times more likely than a viable pregnancy.
Ultrasound measurements of the yolk sac or fetal pole also can help diagnose early pregnancy loss, but these are more variable and thus less helpful than gestational sac measurements.
Studies have shown that when no embryo is seen with a mean gestational sac diameter of 2 mm, a diagnosis of early pregnancy loss will be false in 0.5% of cases in which no yolk sac is seen and in 0.4% of cases with a yolk sac. The false-positive rate approaches 0, however, with a mean gestational sac diameter of 21 mm, she said.
Several studies have shown that an inability to find cardiac activity when the fetal pole measures 5 mm does not confirm a diagnosis of early pregnancy loss because 8.3% of cases will be false positives under those criteria. A fetal pole measuring at least 5.3 mm with no cardiac activity, however, eliminates the possibility of a false-positive diagnosis.
The criteria released by the Society of Radiologists in Ultrasound express concern about the difficulty for an average ultrasonographer to detect fractions of millimeters in differences, so they allow a margin of error. The cutoff for a diagnosis of early pregnancy loss is extended to a mean gestational sac diameter of 25 mm with no embryo, or a fetal pole measuring 7 mm with no cardiac activity.
Dr. Steinauer reported having no relevant financial disclosures.
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