Lower β-HCG Threshold For Pregnancies of Unknown Location?


COPENHAGEN — Roughly 20% of pregnancies currently regarded as failing intrauterine pregnancies may actually be viable, results of a prospective, observational study suggest.

Serum HCG guidelines for recognizing intrauterine pregnancy viability should be revised to reflect this information, Emma Kirk, M.D., said at the annual meeting of the European Society of Human Reproduction and Embryology.

Evidence suggests that about one-third of pregnancies of unknown location (PUL) are actually intrauterine pregnancies that are too small to visualize on transvaginal ultrasound. Guidelines issued by the American Society for Reproductive Medicine advise that in such cases a suboptimal rise in the β-HCG level—defined as a rise of less than 66% over 48 hours or an HCG ratio (HCG at 48 hours to HCG at 0 hours) of less than 1.66—is predictive of nonviability, Dr. Kirk said.

In many cases, such HCG findings would prompt an intervention, such as laparoscopy, to look for a possible ectopic pregnancy, but clinicians should be aware that in some cases this could interrupt a viable pregnancy, said Dr. Kirk of the early pregnancy unit at St. George's Hospital, London.

In a prospective, observational study of 985 PULs in her unit between June 2001 and October 2004, Dr. Kirk's team documented 115 (12%) with suboptimally rising HCG. Of these 115 pregnancies, 31% were eventually identified as intrauterine pregnancies, 43% were ectopics, and 26% were “failing,” that is, HCG levels had begun to decrease.

The mean HCG ratio in the intrauterine pregnancy group was 1.46. While most of these pregnancies (81%) eventually failed, 19% remained viable. Among these viable pregnancies, the lowest HCG ratio was 1.33 and the mean was 1.56.

“PULs with suboptimally rising HCG should be managed conservatively because interventions when the HCG ratio is as low as 1.33 could interrupt a viable pregnancy,” Dr. Kirk said.

She said the pregnancy unit she works in attempts interventions in such pregnancies only if the patient has symptoms.

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