Hallow Dear, Your doubt is valid. Phenobarbital has been assigned to pregnancy category D by the FDA. An increased risk of congenital malformations has been associated with use of phenobarbital during pregnancy. I would not advise you to take this medicine during pregnancy. Phenobarbital should only be given during pregnancy when there are no alternatives and benefit outweighs risk. In fact, Phenobarbitone might have been prescribed to you so that you take good bed rest. I feel you should drop these tablets and take bed rest without any sedatives. This is not a must medicine for the treatment of threatened abortion. Instead, you may start taking Tab. Sustain which is a Progestational medicine and will help stabilizing your pregnancy. I hope you got the message. Dr. Nishikant Shrotri