I had the tdap shot, back to back, two years in a row, one while not pregnant and one while pregnant. i'm reading that it could be harmful. is that so?

Fine: Having 2 dtap shots in 2 years should be fine.

No: The only bad thing is that you are more likely to have an increased local reaction where your arm is sore a bit more than if you just had one dose. There is absolutely no other problem with getting doses in back to back years. Many OB's are now giving during each pregnancy to help protect the newborn from whooping cough by boosting maternal antibodies.