Even low levels of smoking can make getting pregnant more difficult and is harmful to your pregnancy. Smoking one - five cigarettes a day, for example is a risk factor for ectopic pregnancy. Smoking less cigarettes does nothing to bring down the the risk of premature birth or low birthweight.
Low-tar or low nicotine cigarettes are just as harmful to you and your baby’s health.
If you stop smoking before becoming pregnant, then all your risks will become as low as for women who have never smoked.