Smoking!!

Does smoking effects pregnancy??? I need hep!
M a chain smoker and I smoke more that 15 cigs a day.. I have a great sex life... M with this man from past 4 years who love me immensely and we are getting married this September.. I know smoking is a bad habit and I've tried quitting it but.... Phew!
It's lately bothering me! Is it a myth or fact??