Tdap shot

I remember getting the shot back in 2012 while in the hospital after having my son. I had my daughter in 2013 but can't remember getting it. Now pregnant with my third and I'm supposed to get it on the 15th and I'll be 31weeks. I asked if I could get it after delivery like I did with my son and she said no you have to get it while pregnant. Is this shot safe to get while being pregnant?