Pregnancy is a normal physiological state accompanied by significant hormonal, mechanical and circulatory changes. Changes in respiratory physiology during pregnancy occur due to structural changes in the chest wall and abdominal compartments as a consequence of hormonal changes, enlarging uterus and elevated diaphragm. Though there are changes in certain respiratory parameters, FEV1 and PEFR are largely unaffected. It is essential that the normal physiological changes in the respiratory system have to be kept in mind to enable accurate diagnosis of respiratory impairment in pregnancy. PEFR is a simple, non-invasive, easily performable, portable, economical and reproducible tool for effective assessment of asthma control. Though PEFR has been postulated not to significantly change throughout pregnancy, there are conflicting reports from various studies on the variation of PEFR in pregnancy. Hence based on above findings the present study was planned for Study of Pulmonary Parameters like FVC and PEFR in Pregnant Females and Its Correlation with Progesterone Levels. The present study was planned in Department of Physiology, Patna Medical College, Patna, Bihar from January 2019 to May 2019. Total 80 cases were enrolled in the present study. The 20 cases are of non-pregnant females. The 20 cases are of each 1^stTrimester, 2^ndTrimester and 3^rdTrimester cases. FVC & PEFR was performed using Mini Wright s Peak Flow Meter and best of three recordings noted. Data analyzed using SPSS package version 21.0. Association between PEFR with Age and BMI performed using Pearson correlation. The data generated from the present study concludes that definite alteration in pulmonary parameters during different trimesters of pregnancy. The same study involving larger population would help us more in deriving the norms on predicted values on pulmonary parameters in pregnancy.