Of the inhaled corticosteroids, budesonide is currently the only one that is category B.
The category assignment was based on the findings of a 1999 study of 2,014 records in the Swedish Medical Birth Registry, which showed no increased risk for congenital malformations, premature birth, low birth weight, C-section, stillbirth, or multiple births associated with the use of budesonide during pregnancy (Obstet. Gynecol. 93:392-95, 1999).
Inhaled corticosteroids called top Tx option in pregnancy; moderate, persistent asthma. OB/GYN News, Sept 1, 2003 by Kerri Wachter.
Asthma and pregnancy. JACI, 2011.