Morning sickness would be the only issue. And that is totally unpredictable. For the first three months I was a total mess. The one time I flew during the first semester I was completely miserable, but then I was completely miserable 24/7!
If you are worried and you do get sick, speak to your health care provider. There is safe medication available that will help with nauseau. The home remedy touted is ginger, I can't stand ginger, but the medication ( I took zofran and one other, can't remember the name) was a life saver.