Suspected Pulmonary Embolism in Pregnancy
A 29-year-old woman at 24 weeks' gestation presents with sudden-onset pleuritic chest pain and dyspnea. Heart rate is 112/min, blood pressure 118/74 mmHg, respiratory rate 22/min, and oxygen saturation 94% on room air. D-dimer is elevated. She has no prior VTE, no known thrombophilia, and no renal disease. The emergency physician asks for a CT pulmonary angiogram. The obstetric team is concerned about fetal radiation and asks whether ventilation–perfusion (V/Q) scanning or another strategy is preferable. The department has both CT and nuclear medicine available, and the patient is hemodynamically stable.
1. How should the choice between CTPA and V/Q scanning be reasoned through in pregnancy?
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- Both studies are acceptable in pregnancy when indicated; the choice should be individualized rather than dogmatic.
- CTPA generally gives a definitive diagnosis or exclusion, is widely available and rapid, and delivers a lower fetal dose than V/Q in many protocols (fetal dose roughly in the low-milligray range vs higher for V/Q depending on agent and protocol). Its main downside is maternal breast dose and the small theoretical risk of contrast in pregnancy (iodinated contrast is generally considered acceptable; neonatal thyroid effects are a concern mainly with free iodide loads, and current guidance supports use when needed).
- V/Q avoids iodinated contrast and breast dose but delivers a higher fetal dose in many protocols and is less often definitively diagnostic (non-diagnostic rates are higher, especially with a normal chest radiograph and no prior V/Q for comparison).
- Practical algorithm: if the chest radiograph is abnormal, CTPA is usually preferred; if normal, either may be used, and local expertise/protocol matters. In this hemodynamically stable patient, CTPA is a reasonable first choice given its diagnostic yield and lower fetal dose in most protocols.
- The most important point: do not withhold a needed study because of fetal dose concerns; untreated PE is far more dangerous.
2. What radiation-protection counseling would you give the patient?
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- Explain that the fetal dose from a properly performed CTPA is small (typically well below thresholds associated with deterministic effects) and that the study is being done because a missed PE could be life-threatening to both mother and fetus.
- Note that no single diagnostic study approaches the dose range associated with fetal harm; deterministic effects are not expected at these doses.
- Mention that shielding and protocol optimization (limited scan range, reduced tube current) are used, and that the maternal breast dose is a consideration but not a reason to avoid a needed diagnosis.
- Document the discussion.
3. If the CTPA is negative, what else should be considered, and how does that affect the imaging strategy?
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- Consider alternative diagnoses: pneumonia, pleural disease, pulmonary edema, or musculoskeletal pain; a chest radiograph and clinical review are useful.
- If clinical suspicion remains high despite a negative CTPA, further evaluation (e.g., lower-extremity ultrasound for DVT, or repeat imaging if symptoms progress) may be warranted.
- This reinforces that the initial test should be the one most likely to be definitive in that patient - a non-diagnostic V/Q would leave the question unresolved and may require CTPA anyway, adding dose.