There are a lot of reasons to kick the habit, but none as powerful as preparing for pregnancy. Smoking makes it harder to get pregnant by lowering your estrogen levels, says Mary Jane Minkin, M.D., co-author of The Yale Guide to Women's Reproductive Health. And of course, once you become pregnant, smoking exposes your baby to nicotine, carbon monoxide, and tar, all of which decrease the amount of oxygen she gets. Women who smoke during pregnancy are more likely to have serious complications, including stillbirth. And their babies are more likely to be born prematurely, underweight, and with birth defects such as cleft lip or palate. You can do it -- your future child will be so proud of you. Find help for getting started here.