Background & Objectives: The aim of the present study was to monitor the changes that occur in pulmonary function tests in the different trimesters of pregnancy as compared with that of control group i.e., non pregnant women. Materials & Methods: The study consists of recording the Pulmonary Function Tests of four groups of female subjects including pregnant women of various phases of gestational period i.e., 12 weeks, 24 weeks 36 weeks and control group of non pregnant women using computerized Medspiror. The different static lung function parameters measured in this study were vital Capacity (VC), FEV1 and Peak Expiratory Flow Rate (PEFR). PEFR was measured with Mini Wright’s peak flow meter. Results: We observed a statistically significant decrease in PEFR (p < 0.0001), a significant increase in VC & no significant change FEV1 in different trimesters of pregnancy. Conclusion: Comparative study of pulmonary function tests on different trimesters of pregnancy showed that different respiratory parameters like PEFR were compromised significantly due to mechanical pressure of gravid uterus, diaphragm restricting the movement of lungs. VC showed a significant increase in different trimester’s when compared with the non pregnant state whereas FEV1 showed no significant change. The respiratory system undergoes physiological and anatomical changes during pregnancy and we observed a significant decrease in PEFR and increase in VC among pregnant women.