What will happen if you have one cigarette while pregnant in the last trimester?

Nothing. Don't be crazy. I know this is a stressful time and everyone around you is saying don't do this and don't do that. Well meaning friends will try to save you from the various pitfalls that can harm your baby. But sometimes you find yourself overwhelmed to the point you start questioning and freaking out about everything. I myself almost considered at one point terminating my pregnancy because i had touched some soil with my ungloved hand. Never mind the hot baths I had been taking. But sanity prevailed with the help of a phonecall from my dad. "There are 6500 billion people on this planet. Do you really think if babies were that delicate, there would be that many of us roaming around the planet." Enough said. Good man, my father. I cling to these Words everytime someone says "oh my GOD, you didn't eat soft cheese, did you?!?!?" Don't smoke while pregnant. But if you do, and especially if you just had one, for heaven sake, don't beat yourself up about it.