If you smoke, you are more than 3 times more likely to have a baby who weighs too little at birth than people who don't smoke. You also are more likely to have a lower-birth-weight baby if you are exposed to secondhand smoke while pregnant. Babies born too small or too early can have more health problems. They are also more likely to need special care after birth. Low-birth-weight babies who are born to people who smoke also are at higher risk for illness and death.

The average length of pregnancy is 40 weeks. A preterm baby is born before 37 weeks. Cigarette smoke has thousands of chemicals in it. Many of these chemicals are toxic. Nicotine and carbon monoxide are two of the chemicals that may harm the developing baby. These chemicals can keep food and oxygen from reaching the growing baby.

A baby’s lungs and airways are small. Breathing smoke-filled air makes it hard for the baby to breathe. It can cause lung problems such as pneumonia and bronchitis and make it more likely for children to develop asthma and ear infections. Children of parents who smoke may lag behind in school. They may also be smaller than children whose parents don't smoke. That’s because babies born to people who smoke during pregnancy and who are exposed to secondhand smoke after birth can have weaker lungs. Secondhand smoke is smoke from a burning cigarette. It can also be smoke that a smoker breathes out.

SIDS is the unexplained death of an infant. A baby born to a parent who smoked during and after pregnancy has an increased risk for SIDS.

Studies suggest that regular exposure to secondhand smoke may slow down the growth of the fetus. This makes it more likely for a baby to be born low birth weight. Thirdhand smoke is also harmful. This is the smoke that sticks to objects like walls and curtains. This smoke contains chemicals that are harmful during pregnancy and to babies and children.

Babies born to people who smoke during pregnancy are more likely to have these birth defects:

• Clubfoot
• Opening in the lip (cleft lip)
• Opening in the roof of the mouth (cleft palate)

Smoking increases the risk for an ectopic pregnancy. This happens when the embryo becomes implanted in a fallopian tube or another place outside the uterus.

Nicotine can be passed on to a baby through breastmilk.