I quit with both of my pregnancies... mostly because it was the most nauseating thing ever.
My son as soon as I was downstairs at the hospital I wanted a cigarette... that was after 9 months without.
My daughter, the last day I breastfed, I started again... that was after almost 15 months. It's hard, but I don't think it's the nicotine as much as it is the habit itself for me.