Can a pregnant patient with a pre-existing respiratory condition undergo a pulmonary function test?

Can a Pregnant Patient Undergo Pulmonary Function Testing?

Yes, pulmonary function testing is safe and appropriate during pregnancy, particularly for monitoring pre-existing respiratory conditions like asthma and cystic fibrosis. PFTs involve no radiation exposure, no contrast agents, and pose no risk to the developing fetus 1.

Clinical Indications for PFT in Pregnancy

Chronic Respiratory Disease Monitoring

• Women with cystic fibrosis should undergo monthly PFTs during the first and second trimesters, increasing to every 2 weeks or more frequently as clinically indicated 1
• Higher pre-pregnancy FEV₁ values predict better pregnancy outcomes and complete postpartum lung function recovery 1
• More frequent monitoring is warranted for severe disease (FEV₁ <50% predicted) 1

Asthma Management

• Serial spirometry (FVC and FEV₁) can be performed safely throughout pregnancy and the puerperium to assess respiratory obstruction 2
• Optimal asthma management during pregnancy may oppose the negative effects of advancing gestation on lung function 3
• PFT results guide adjustments to respiratory therapies and physiotherapy regimens as pregnancy progresses 1

Technical Considerations for Testing

Patient Positioning

• Upright sitting is the most comfortable and appropriate position for PFT during pregnancy, especially in later trimesters 1
• Avoid supine positioning after 20 weeks gestation to prevent inferior vena cava compression by the gravid uterus, which decreases venous return and cardiac output 1, 4
• Left lateral positioning optimizes cardiac output if upright positioning is not feasible 4

Expected Physiological Changes

Normal Pregnancy Alterations

• FVC decreases progressively throughout pregnancy (mean values: 2.13 L first trimester, 1.93 L second trimester, 1.90 L third trimester vs. 2.59 L in non-pregnant controls) 5
• FEV₁, PEFR, and FEF 25-75% all show significant decreases compared to non-pregnant values 5, 6
• FEV₁% typically remains stable, though absolute values decline 5
• Functional residual capacity decreases by approximately 20% due to upward diaphragmatic pressure from the growing uterus 4

Interpretation Caveats

• These physiological decrements represent normal adaptation to pregnancy, not pathology 5, 6
• The pattern suggests extrapulmonary restriction from advancing pregnancy rather than intrinsic lung disease 3
• In women with asthma, advancing gestation may have different effects on FEV₁% and FEV₁:FVC% trajectories compared to women without asthma 3

Clinical Value

Avoiding Misdiagnosis

• Understanding normal pregnancy-related PFT changes prevents misdiagnosis and unnecessary interventions 5
• Serial monitoring helps distinguish physiological pregnancy changes from pathological deterioration 6, 2

Risk Stratification

• PFTs help identify cases of restriction or obstruction early, allowing proper management to prevent deterioration 6
• Patients with active asthma and spirometric evidence of obstruction during pregnancy tend to have smaller babies than those in remission 2

Important Distinction from PE Workup

While PFTs are safe and useful for monitoring chronic respiratory conditions, they play no role in evaluating suspected pulmonary embolism during pregnancy 7. For pregnant patients presenting with acute dyspnea, chest pain, or other concerning symptoms suggesting PE, the diagnostic approach involves imaging studies (chest X-ray, lower extremity ultrasound, V/Q scan, or CTPA) rather than pulmonary function testing 7.