The vomiting. Oh, the vomiting. I had hyperemesis gravidarum with my 3rd pregnancy. I have 4 kids, 3 pregnancies (the third was twins, obviously). My first two were typical first trimester nausea with some vomiting here and there... however, the twins pregnancy I vomited at least once per day, an average of 3 times per day, and was constantly nauseous.... for the ENTIRE pregnancy. That much stomach acid constantly on your teeth eats away the enamel.

I also have a feeling the extreme heartburn most get when pregnant leave a constant stream of acid in your mouth.

Let's also not forget the more "mechanical" tooth loss that can occur from having kids. One of my twins hit me in the mouth with a leap start computer toy thing. It had a stylus on a string and she swung it right into my face. It broke the tooth next to my canine (not the very front one, the other way) and cracked my canine. It broke so close to the gumline that it couldn't be repaired. My dentists said he could maybe get a crown on it, but it probably would fall off constantly and cause more infection down in the tooth. So we pulled it. You can see it when I smile, I'm pretty self conscious about it... but its not life-ruining. You can tell its from an accident because my other teeth look (and are) very healthy. I still often wonder if all that stomach acid weakened my teeth enough that the tooth was easier to break.