Smoking while pregnant

So I keep seeing posts about smoking while pregnant. I am a heavy cigarette smoker and while I fully understand that it is a hard addiction to quit I just don't understand how some women can think that it is okay to continue to smoke while they know they are pregnant. Being a parent means putting your child's needs and wellbeing above everything else. No matter what that might be. Like I said I am a heavy smoker but as soon as I found out I was pregnant I stopped on the spot. I miscarried but for those three months that i was pregnant I didn't even think about picking up a cigarette, knowing that that might harm my baby. I just can't understand how some people would put their unborn child at risk for something that doesn't even help their own bodies. Please if you are pregnant and a smoker do yourself and your baby a favor and try as hard as you can to quit, I know it might be hard at first but it'll get easier.