Pregnancy of unknown location occurs in 10% of pregnant patients undergoing transvaginal ultrasound in the first trimester
Patients presenting with a positive pregnancy test and vaginal bleeding or pelvic pain routinely undergo transvaginal ultrasound as the standard diagnostic assessment. Pregnancy of unknown location is a classification that describes patients with a positive beta-human chorionic gonadotropin (β-hCG) test without ultrasound findings of intra- or extrauterine pregnancy.1–3 The pregnancy of unknown location may be a viable or nonviable intrauterine pregnancy or ectopic pregnancy, or may resolve without its location ever being identified.1–3
Gynecology consultation is indicated if history and physical examination at any encounter suggest ectopic pregnancy
Ectopic pregnancy occurs in 8%–14% of pregnancies of unknown location, compared with 2% in all pregnancies,3 but risk of rupture is low (2–3/1000 pregnant people).4 Asymptomatic patients should receive written information outlining symptoms that should prompt medical attention; an information sheet is provided in Appendix 1 (available at www.cmaj.ca/lookup/doi/10.1503/cmaj.200142/tab-related-content).5 Persistent or worsening pain, signs and symptoms of hemodynamic compromise or hemoperitoneum require urgent evaluation.1,5
All patients with pregnancy of unknown location require a repeat β-hCG test 48 hours after initial testing
The ratio between 2 β-hCG measurements 48 hours apart stratifies risk of ectopic pregnancy. 1,2,5 A ratio greater than 1.63 suggests an intrauterine pregnancy, and patients should have a repeat transvaginal ultrasound in 1 week. A ratio of less than 0.5 suggests a failing pregnancy of unknown location that will resolve without intervention. All that is required is a serum β-hCG test in 14 days to ensure pregnancy resolution, and repeat transvaginal ultrasound is not indicated. Ratios between 0.5 and 1.63 are red flags, carrying a risk of ectopic pregnancy greater than 5%. Close follow-up in 48 hours with repeat transvaginal ultrasound and β-hCG is essential.2 A management algorithm with thresholds, adapted from the National Institute for Health and Care Excellence in combination with management suggested by Tommy’s National Centre for Miscarriage Research, is presented in Appendix 2 (available at www.cmaj.ca/lookup/doi/10.1503/cmaj.200142/tab-related-content).2,5
Empiric definitive management of pregnancy of unknown location is rarely warranted
Empiric management with methotrexate or laparoscopy before follow-up evaluation may result in harm to an intrauterine pregnancy, or unnecessary laparoscopy in pregnancies that will ultimately resolve without intervention.1,2
Expectant management of pregnancy of unknown location is safe, provided there is consistent follow-up
All patients, including those with low-risk pregnancies of unknown location, must be followed by the same health care team until the β-hCG test becomes negative or the pregnancy location is identified.1–3
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Footnotes
Competing interests: None declared.
This article has been peer reviewed.
References
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