MRI for Knee Concerns in the Third Trimester of Pregnancy
MRI without contrast is safe for evaluating knee problems during the third trimester of pregnancy and should be performed when clinically indicated. 1
Safety Profile of Non-Contrast MRI
MRI does not use ionizing radiation and has no demonstrated adverse fetal effects when using standard clinical scanners (1.5T or 3.0T), making it the preferred imaging modality when ultrasound is inadequate. 1 The evidence supporting MRI safety during pregnancy is robust:
- No documented adverse fetal effects have been demonstrated to date with standard clinical MRI 1
- Second and third trimesters are preferred timing windows, and the third trimester falls well within the safe period for MRI examinations 1
- MRI can effectively evaluate musculoskeletal pathology including disc disease, fractures, and soft tissue injuries without requiring contrast enhancement 1
Critical Contrast Agent Considerations
Gadolinium-based contrast agents must be avoided during pregnancy, including the third trimester. 2, 1 The evidence against gadolinium use is compelling:
- Gadolinium crosses the placenta and accumulates in fetal tissues and amniotic fluid 1
- A large cohort study of 1,424,105 deliveries found that gadolinium exposure at any time during pregnancy was associated with increased risk of stillbirth or neonatal death (adjusted RR 3.70; 95% CI 1.55-8.85) and rheumatological, inflammatory, or infiltrative skin conditions (adjusted HR 1.36; 95% CI 1.09-1.69) 3
- For knee imaging specifically, non-contrast MRI is sufficient for diagnostic purposes 1
- Gadolinium should only be considered in exceptional circumstances immediately prior to delivery or when termination is planned 2
Practical Implementation
Position the patient in left lateral or left pelvic tilt to avoid inferior vena cava compression during the examination. 1 Additional practical considerations include:
- Perform the examination according to "as low as reasonably achievable" principles to minimize exposure time 1
- Non-contrast MRI spine protocols can be adapted for knee imaging without safety concerns 1
- The third trimester presents no specific restrictions for musculoskeletal MRI when medically necessary 1
Clinical Context
Knee dysfunction is common during pregnancy, with 33.6% of third-trimester patients reporting significant symptoms (IKDC scores <75) 4. Risk factors include high activity levels, history of knee problems, younger age, and elevated BMI 4. When clinical evaluation and physical examination are insufficient to guide management, MRI provides definitive diagnostic information without fetal risk.
Common Pitfalls to Avoid
- Never administer gadolinium contrast for knee MRI during pregnancy - the risks clearly outweigh any potential diagnostic benefit, and non-contrast sequences provide adequate diagnostic information 1, 3
- Avoid supine positioning for extended periods during the examination, as this can cause maternal hypotension and reduced placental perfusion 1
- Do not delay medically necessary MRI due to unfounded safety concerns - the evidence supports its use in the third trimester 1