Why does smoking whilst pregnant harm your baby?

That's why even a "light" habit can have an outsize effect on your baby's health. How smoking affects your baby: Weight and size On average, a pack-a-day habit during pregnancy will shave about a half-pound from a baby's birth weight. Smoking two packs a day throughout your pregnancy could make your baby a full pound or more lighter. read more

Smoking during pregnancy affects you and your baby's health before, during, and after your baby is born. The nicotine (the addictive substance in cigarettes), carbon monoxide, and numerous other poisons you inhale from a cigarette are carried through your bloodstream and go directly to your baby. read more

Good question. Cigarette smoking narrows and constricts the veins and arteries. This is bad enough in an adult, where cigarette smoking is the number one preventable health risk. read more