About 60 to 75 percent of pregnant women have swollen, red, tender gums that bleed when flossed or brushed. This gum inflammation is pregnancy gingivitis, a mild form of gum disease. Pregnancy gingivitis is partly caused by hormonal changes that make your gums more sensitive to the bacteria in plaque.
Essentially, your levels of progesterone and estrogen are incredibly high during pregnancy, and this increases blood flow to your mucous membranes, which leads to sensitivity.
Dr. Banić