It's said that the body will lower it's immune system while the bean is in it's first stages of creation so that your immune system doesn't 'fight off' this 'new intruder'. I had a wicked bad cold leading up to my last pregnancy, but sadly it ended in ectopic with tube removal.
I'm not saying that getting a cold during your TWW is a bad thing. It could be a very good thing, and it is VERY common for pregnant women.
Good luck!!