Have you tried quitting yet to know it's stressful? Not everyone finds it a major source of stress. I've never been a smoker to quit but everyone around me has given up in the past few years and it has been clearly easier on some than others. One of my friends gave up one day after a particularly bad cough, just binned them and that was that (my Dad did the same thing, though sadly his 'cough' turned out to be lung cancer and he died). It might not be as difficult as you think, but living with the effects smoking can have on your baby definitely will.
I've never in my life heard of miscarriage by quitting cigarettes, but I'm going to guess a smoker came up with that nugget. You're going to have to deal with stress throughout your pregnancy, it's just a part of life. It won't harm your baby and neither will quitting.