Got fever and possible slight rash after dpt vaccine in infancy in 1981. havent gotten any pertussis shots since. should i get the tdap vaccine now during pregnancy? what are the risks of getting it? has the vaccine changed since 1981?

Short answer yes.: it is recommended to receive the TDAP during the third trimester of every pregnancy. This imparts protection from pertussis (whooping cough) to the new baby, For your particular case, discuss with your doctor, likely they will proceed with the vaccine, after talking with you.

Some basics: The DPT vaccine used in 1981 was the old whole cell vaccine that routinely eventually had reactions in anyone who use it. What you describe does not sound like those issues but may have been to any component of the mix used at that time. The Tdap has been reformulated. The pertussis is completely new & almost never has associated reactions. Get it in the docs office & stay a while to be monitored