RISE IN ANTIBIOTIC USE IN PREGNANCY. “Over the past 30 years, first-trimester use of prescription drugs increased >60%. In 2010, 94% of pregnant women took at least one medication during pregnancy, and 82% did so in the first trimester; among these medications, antibiotics were within the top 20 most frequently used.”
http://www.nature.com/ijo/journal/v37/n7/full/ijo201347a.html