Physiological changes during pregnancy significantly influence respiratory function, posing potential health risks to the mother and fetus, especially in twin pregnancies. This study aimed to investigate the impact of deep breathing exercises on pulmonary functions in twin pregnant women. The primary objective was to evaluate response of pulmonary functions to deep breathing exercises during the third trimester of twin pregnancies. A randomized controlled study was conducted at Soaad Kafafy University Hospital between October 2022 and June 2023. Sixty twin pregnant women, aged 25 to 35 years, in the third trimester of their pregnancies, were randomly assigned to two equal groups. Pulmonary function tests conducted at the 27th and 36th weeks of gestation to establish baseline values. The study group engaged in deep breathing exercises, involving diaphragmatic and costal breathing, three times daily for 15 repetitions over 9 weeks. Pre-treatment values of Forced Vital Capacity, Forced Expiratory Volume in the first second, and Peak Expiratory Flow showed no significant differences between the study and control groups (p > 0.05). Post-treatment outcomes in the study group demonstrated a noteworthy improvement in all variables compared to pre-treatment values (p < 0.05). Conversely, the control group showed no significant difference between the pre and post study outcomes. Comparative analysis of post-study results revealed a substantial increase favoring the study group (p < 0.05). Diaphragmatic and costal breathing proved to be effective in augmenting pulmonary functions in twin pregnant women. These findings underscore the benefits of incorporating respiratory exercises into prenatal care for twin pregnancies.