Intermenstrual Bleeding Initial Investigation
A 30-year-old sexually active woman with regular 30-day cycles reports 5 days of bleeding between her periods. She uses no contraception. Blood pressure is 118/72 mm Hg and pulse 80 beats/min. Speculum examination shows a normal-looking cervix with blood coming from the external os. Which of the following is the most appropriate initial investigation?
- A.Complete blood count
- B.Serum TSH
- C.Transvaginal ultrasound
- D.Serum beta-hCGCorrect
Explanation
Any abnormal vaginal bleeding in a woman of reproductive age is a pregnancy complication until proven otherwise, so beta-hCG is the first test regardless of how atypical the bleeding pattern appears. Ectopic pregnancy classically presents with irregular or intermenstrual bleeding rather than a missed period, and threatened miscarriage or early pregnancy failure can look identical, so missing the diagnosis risks tubal rupture and haemorrhage. The result also determines the entire subsequent pathway: if positive, quantitative beta-hCG and transvaginal ultrasound are done urgently to locate the pregnancy; if negative, the workup follows the PALM-COEIN framework with pelvic ultrasound, cervical screening and infection testing including chlamydia, and endometrial sampling if risk factors for hyperplasia are present. A complete blood count quantifies the consequences of bleeding but not the cause. Thyroid dysfunction and coagulation disorders are genuine causes of abnormal uterine bleeding and are tested later in the sequence. Transvaginal ultrasound is a valuable early imaging study but is far less informative and potentially misleading if the pregnancy status is unknown. A normal-looking cervix does not exclude cervical pathology, so cytology and infection screening remain part of the later workup.
Why each option
- A.
- A complete blood count measures the impact of blood loss and may screen for thrombocytopenia, but it does not identify the cause of the bleeding.
- B.
- Thyroid dysfunction can cause abnormal uterine bleeding and is worth testing, but only after pregnancy has been excluded.
- C.
- Transvaginal ultrasound is an important early step in the workup but should follow, not precede, the pregnancy test, which determines how the images are interpreted.
- D.
- Correct. Beta-hCG excludes ectopic pregnancy, miscarriage and early intrauterine pregnancy, and is the first test in any reproductive-age woman with abnormal bleeding.
Reference: FIGO PALM-COEIN classification, 2018; UpToDate 2025, Abnormal uterine bleeding in reproductive-age women
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