The essential pregnancy hormone progesterone is indirectly responsible for pregnancy gingivitis. Progesterone leaves the gums more sensitive to oral bacteria that cause bleeding and painful gums. On top of that, pregnant women have a higher volume of blood circulating around their body, and this can further contribute to painful gums. Typically, women who have gingivitis will notice bleeding when they brush and floss their teeth, but bleeding can also start spontaneously. Around half of all pregnant women have painful gums at some point, while they are expecting.
Most dentists will tell you that painful and bleeding gums are not in fact caused by hormones, but by poor dental and oral hygiene. After all, it is bacteria that cause gingivitis, and not hormones so they argue. While they certainly have a point and are technically right, the hormonal changes that take place in the body during pregnancy do give bacteria a much better chance to get a grip on your gums. You can react to this by brushing your teeth more often, and making sure that your oral hygiene is the best it can possibly be. Use a soft brush, and make sure to brush your gums too. Floss on a daily basis and see a dentist as soon as you spot signs of trouble. For more information about dental care during pregnancy, see going to the dentist while pregnant what you need to know.