Provided is a composition for the treatment of pregnancy-associated diseases, and more particularly, to a pharmaceutical composition for the prevention or treatment of premature delivery or breast cancer. The pharmaceutical composition including extracellular vesicles derived from bacteria belonging to the genus Bacillus as an active ingredient may induce pregnancy or prevent premature delivery of pregnant women, may be used to prevent or treat pregnancy-associated diseases such as breast cancer, and may be used to diagnose a risk of premature delivery by measuring the amount of extracellular vesicles derived from bacteria belonging to the genus Bacillus in pregnant women.