I will let science decide.
http://www.askdrsears.com/html/10/T105800.asp
Consider the physiological effects of smoking on yourself and your baby, especially the increased risk of SIDS.
1. It retards growth. Smoking stunts the growth of the developing fetus. Nicotine narrows the uterine blood vessels, thus reducing blood flow to the baby.
2. It retards brain development. Nicotine has been shown experimentally to retard fetal brain growth in animals. The developing brain is particularly vulnerable to low levels of oxygen, and immaturity of the brain center that regulates breathing could contribute to SIDS.
5. Passive smoking also harms the baby. When expectant mothers are exposed to smoke from other people's cigarettes, their babies are also exposed. One study showed that a pregnant woman's exposure to smoke for at least two hours a day doubled her risk of delivering a low birthweight baby. While older studies claimed no increased SIDS risk if the father smoked, a newer study reports a higher risk of SIDS if the father smokes. Demand that your husband and co-workers respect the life inside your womb. If your job requires working in a smoke-contaminated environment while pregnant, know that this is a proven health hazard to your baby and is grounds for reassignment to a baby-healthy environment. As a testimony to the wisdom of the body, many mothers find they have an aversion to being around cigarette and cigar smoke (and to drinking alcohol) while pregnant. Listen to the warnings of your body and hundreds of medical studies: Don't expose yourself and your baby to smoke while pregnant. Legally, you have the right to work in a smoke-free environment.
6. Smoking harms mothers and babies.
Increases infertility (smoking could account for ten percent of infertility problems in mothers)
Increases risk of ectopic pregnancy
Increases risk of placenta previa
Increases risk of premature separation of the placenta
Increases risk of placental abnormalities (known as "smoker's placenta")
Increases risk of problem pregnancies, e.g., pre-eclampsia
Increases risk of prematurity under intrauterine growth retardation
Increases risk of the newborn dying at birth by twenty percent; thirty-five percent if mother smokes more than thirty-five cigarettes a day
Increases risk of respiratory infections in infant
Increases risk of SIDS by two to five times