I would just approach it as a risk-benefit situation that you're now aware of... make sure he explains to you why he thinks you're in pre-term labor vs. Braxton Hicks if the contractions are acting just like BH's do?
I had to take a Category C anti-malarial (chlorequin) in 1st trimester of my last pregnancy, and DD is perfect. The risk of not taking it was worse than the risk of taking it, and so I took it. I was nervous but everything was fine.