Smoking is the most common form of substance abuse in pregnant women. The incidence of smoking in pregnancy is between 10-50%. The incidence is higher in socially deprived populations. Smoking incidence decreases by 30% throughout pregnancy due to voluntary cessation.
Smoking in pregnancy affects the placental function. The placenta is the source of blood flow, oxygen and nutrition to a pregnancy. Women that smoke have a higher incidence of placental malfunction. Because of these effects, women who smoke have a higher risk of miscarriage, placental abruption (premature separation of the placenta from the uterus), placental insufficiency (may lead to poor blood flow and oxygen flow to the fetus), low birth weight infants, and higher incidence of placenta previa (when the placenta blocks the cervix-requiring C-section birth). There are also reports of higher incidence of neonatal death and SIDS (sudden infant death syndrome) in newborns of women who are smokers during pregnancy.
The above risks increase with the increasing number of cigarettes smoked per day. Second hand smoke does have an impact and is equal to smoking about 1-5 cigarettes per day (for every pack to half pack of exposure). Babies born to mothers who are smokers have more abnormalities on neurological exam in comparison to babies of nonsmoking mothers. There is also a higher rate of asthma and ear infections in children who have mothers that were smokers in pregnancy.
When reading the above risks it is obvious why women are encouraged to refrain from smoking during pregnancy. Our role as obstetricians should be to provide encouragement and support to our patients because smoking is a difficult addiction to overcome.