Methods: The study population was pregnant women with gestational age of 28 weeks. The sample comprised 52 pregnant women aged 18 to 35 years. The subjects were randomly divided into the intervention and control groups. The intervention group performed specific breathing exercises 3 times a day, each time 15-20 minutes for 10 weeks. In this period, the control group did not receive any training program. Pressure of End Tidal Carbon Dioxide (PETCO2) was measured using capnography device before and after this period in both groups. Data were analyzed using SPSS 16 software. Kolmogorov-Smirnov test was used to examine normal distribution of the data. In order to study the changes within each group, paired t-test was used and for comparing the groups, Independent t-test was used. P <0.05 was considered as the significant level. 

Results: Comparison of PETCO2 of two groups before performing breathing exercises showed that mean PETCO2 in the intervention group was 1.08 mmHg less than the control group.This difference was not significant (P= 0.308). However, after performing breathing exercises, mean PETCO2 in the intervention group was 2.34 mmHg higher than the control group, which showed a significant difference (P= 0.011). 

Conclusion: According to these results, performing breathing exercises increases the amount of PETCO2 and pushes it toward the normal range in pregnant women. Therefore, these exercises can help modify breathing patterns in pregnant women, and has a significant role in fetal and maternal health.