Suspected Ectopic Pregnancy: Initial Imaging
A 19-year-old primigravida presents with lower abdominal cramping and light vaginal bleeding. Her last menstrual period was 6 weeks ago and the pregnancy test is positive. Blood pressure is 112/70 mm Hg, pulse 92 beats/min, temperature 36.9 °C. Pelvic examination shows a closed cervical os with marked pain on moving the cervix and right adnexal tenderness. Which of the following is the most appropriate next step?
- A.Perform a transvaginal ultrasoundCorrect
- B.Order a complete blood count
- C.Order CT of the abdomen and pelvis
- D.Repeat a deeper bimanual pelvic examination
Explanation
Cervical motion tenderness and adnexal tenderness in a woman who is 6 weeks pregnant with a closed os make ectopic pregnancy the leading concern, and transvaginal ultrasound is the definitive next investigation. It locates the pregnancy, identifies an adnexal mass or tubal ring, detects free fluid suggesting haemoperitoneum, and confirms or excludes an intrauterine sac; a pseudogestational sac must not be mistaken for a true one. A complete blood count is a reasonable adjunct for baseline haemoglobin but does not tell you where the pregnancy is and would not change immediate management. Computed tomography exposes the pregnancy to ionising radiation, is far less sensitive than ultrasound for early gestation, and is not the imaging modality of choice in first-trimester pelvic pain. Repeating a deeper bimanual examination adds no information and can provoke pain or, in theory, disturb a fragile tubal pregnancy. If ultrasound is inconclusive the pathway becomes serial beta-hCG at 48 hours with repeat imaging, the standard approach to a pregnancy of unknown location. Rhesus status should be determined and anti-D immunoglobulin given when indicated. The patient must be warned to return urgently for severe pain, shoulder-tip pain or fainting.
Why each option
- A.
- Correct. Transvaginal ultrasound localises the pregnancy and detects an adnexal mass or free fluid.
- B.
- A blood count gives baseline haemoglobin but does not establish the location of the pregnancy.
- C.
- Computed tomography irradiates the pregnancy and is less sensitive than ultrasound in early gestation.
- D.
- Repeating the bimanual examination adds no diagnostic information and worsens pain.
Reference: ACOG Practice Bulletin No. 193, Tubal Ectopic Pregnancy, reaffirmed 2022
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