"False positive" urine pregnancy test results after successful medication abortion

Abstract

Objective: To examine the proportion of high-sensitivity urine pregnancy test (HSPT) results that were positive by time after successful medication abortion.

Study design: We used data from an ongoing study that provides mifepristone and misoprostol for medication abortion by direct-to-patient telemedicine and mail. Providers evaluated abortion outcomes by patient interview and clinical tests per clinical judgment and participant preference. We identified all participants enrolled July 2016 to September, 2020 who had an HSPT result and no indication of viable pregnancy after treatment. We used logistic regression to examine the association between the timing of the initial post-treatment HSPT, gestational age, and the proportion of HSPTs that gave a positive result.

Results: Of the 472 participants in our analysis, 88 (19%) had positive initial HSPTs. The proportions that were positive at ≤20 days, 21 to 27 days, 28 to 34 days, and ≥35 days after mifepristone ingestion was 14 of 29 (48%), 15 of 58 (26%), 49 of 258 (19%), and 10 of 127 (8%), respectively (p < 0.001). Gestational age at mifepristone ingestion was not significantly related to positive HSPT results (p = 0.28). Multivariable logistic regression confirmed both findings and did not identify a statistically significant interaction between these variables. In the 67 participants who relied solely on further HSPTs to confirm abortion outcome, the median interval between the initial positive test and first negative test was 14 days.

Conclusions: The proportion of participants with positive HSPTs declined with time after successful medication abortion. However, nearly one-fifth of participants with complete abortion had positive tests 4 weeks after treatment.

Implications: HSPTs provide an inexpensive, convenient option for confirming success of medication abortion at home. However, a substantial minority of patients without ongoing pregnancy have positive HSPT results. Development of a symptom-based strategy for medication abortion outcome assessment without any confirmatory tests should be a priority.

Keywords: False positive; Gestational age; High-sensitivity urine pregnancy test; Medication abortion.