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Three Part Question

In [pregnant women] presenting to the ED with a suspected PE are [ventilation/perfusion scans, (V/Q) and/or CTPA tests] as diagnostic tools [harmful to the foetus]?

Clinical Scenario

A 31-year old pregnant woman presents to the ED with a query PE. Results of the D-Dimer test come back as high. You decide that further investigations are required before you can safely exclude a PE. Both V/Q and CTPA is available to you at that time, but you question how harmful they will be to the foetus and whether you should avoid ordering such tests.

Search Strategy

Cochrane Database of Systematic Reviews 2nd Quarter 2008. EMBASE 1996 to 2008 week 25. Medline 1950-Week 2 June 2008 using the OVID interface. CINAHL 1982 to June Week 2 2008
([{pregnanc$.mp. OR exp Pregnancy OR exp Pregnancy Complications or pregnant.mp. OR exp Pregnant Women}] AND [exp Pulmonary Embolism OR pulmonary embolu$.mp. OR pulmonary embolus.mp. OR exp Venous Thrombosis/ pleuri$.mp. OR pulmonary embol$.mp.]) AND {ventilation perfusion scan$.mp. OR pulmonary scinitigraphy$.mp. OR lung scintiscanning$.mp. OR pulmonary scintigraphy.mp. or exp Tomography, Spiral Computed/ OR exp Tomography, X-Ray Computed/ or CT pulmonary angiography$.mp.} AND {exp Fetus/ or foetus$.mp.}
LIMIT to human AND english.

Search Outcome

176 papers found of which 174 were irrelevant.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Loon AJ et al. 2007 The Netherlands	Systematic review of clinical trials and reviews. Sixteen references of papers used.	Systematic Review.	Level of radiation exposure for the following variables:		Search strategy could have been wider to include a greater part of the grey literature. The review does not state between which period the searches were conducted over. No exclusion criteria was given.
			Upper limit that causes injury to the foetus	<10mSv
			For teratogenesis	<100mSv
			Future Malignancy risk in unborn child	<10mSv
			Reduction in IQ	>100mSv
			Perfusion scintigraphy	0.2 mSv
			Ventilation scintigraphy	0.3 mSv
			CTPA Femoral route	3.74 mSv
			CTPA Brachial route	<0.5 mSv
Kennedy et al 2006 UK	A modified anthropomorphic phantom containing a 15cc ionisation chamber at the site of the uterus to allow the dose of radiation to the foetus to be measured. The effects of lead shielding were explored by varying the thickness of the lead and the distance between the foetus and radiation dose.	Prospective experimental Study. (Level 2c)	Recommended thickness of lead shield w/o compromising comfort	<0.7mm	Study carried out on a phantom, which cannot represent the range of variation in women’s bodies at the time of pregnancy.
			Volume lead shield should cover patient	Greatest volume possible
			Foetal radiation dose with shield	Varies 0-55% depends on the distance between the shield and uterus
			Radiation dose variation with distance.	Exponential increase as edge of scan volume moves closer to the point of measurement

Comment(s)

A good systematic review that supports the view that V/Q scans and CTPA do expose the foetus to ionising radiation but the risk is negligible and extremely unlikely to cause any harm to the foetus. So when investigating PE in pregnancy, the risk of misdiagnosing a PE is greater to the mother than performing such investigations. Sometimes radiologists omit the ventilation portion of the V/Q scan in pregnant subjects, to reduce the level of radiation. If this method is applied then the radiation dose is less than that emitted by CTPA. The issue of radiation exposure to the breast tissue of the woman also plays a deciding factor; CTPA delivers more radiation to the breast than V/Q. `

Clinical Bottom Line

Both V/Q scans and CTPA are safe during pregnancy with CTPA being scans being safer. However the risk of ionising radiation exposure is never great enough to cause damage to the unborn child; even performing both will pose no threat.

References

1. Loon v AJ, Stekkinger E. Diagnosis of Deep Vein Thrombosis and Pulmonary Embolism in Pregnancy and Postpartum: Should we Modify the Usual Diagnostic Strategy? Imaging Dec MRI 2007;11(3):18-22.
2. Kennedy EV, Iball GR, Brettle DS. Investigation into the effects of lead shielding for fetal dose reduction in CT pulmonary angiography Br J Radiol. Br J Radiol. 2007 Aug;80(956):631-8.30