Introduction: Asthma is the most common respiratory disorder to complicate pregnancy and represents a significant public health issue. On many occasions these patients are unable to perform standardized spirometry. The Impulse Oscillometry Technique (IOS) may be suitable in this application since it allows the assessment of airway obstruction by requiring minimum patient cooperation.Aim: Our aim was to identify the relationship between R5, X5, and Resonant Frequency to the 1s forced expiratory volume (FEV1) and forced vital capacity (FVC) in pregnant women.Methods: In 20 asthmatic pregnant patients aged 20-32 yr (mean 26.7 yr) spirometry and Impulse oscillometry (Erich Jaeger, Germany) was performed according to standard guidelines and manufacturer’s instructions. Relationships between spirometric indices and total Resistance (R5), central resistance (R20), peripheral reactance (X5) and Resonance Frequency (FRes) were obtained using correlation and regression analysis. Volumes are expressed in litres and resistance in kpa.1.s.Results: Mean ± SD of FEV1 was 2.7±0.4, FVC was 3.4±0.5, FEV1/FVC was 81.11±8.4, R5 was 0.54±0.15, X5 was -0.16±0.14 and FRes was 0.57±0.19. There was significant (p<0.001) correlation between the FEV1 and R5, X5, Z5 and FRes.R5: FEV1=3.73-1.76R5, R²=0.44; FVC=4.11-1.21R5, R²=0.11X5: FEV1=3.10+1.98X5, R²=0.47; FVC=3.65+1.23X5, R²=0.10FRes: FEV1=3.74-5.13 fres, R²=0.64; FVC=4.28 -4.42 fres, R²=0.26Conclusion: These results suggest that Impulse Oscillometry is a valuable tool to assess airway obstruction as it is simple and requires minimal subject cooperation. This new field of oscillometry application may be particularly useful in patients who are unable to perform spirometry. Further studies are required to determine the sensitivity and specificity of this technique.