Smoking in pregnancy

Smoking adversely affects the fetus and newborn. The effects of smoking are lessened if the mother quits smoking before or during early pregnancy.
Cigarette smoke contains 68000 toxic substances, including nicotine and hydrogen cyanide and toxic heavy metals such as lead and arsenic, all of which readily gain access to the mother’s circulation and cross the placenta. Cyanide lowers the fetus’s ability to use vitamin B12, which is vital to protein formation and the formation of red blood cells. Carbon monoxide which is produced by cigarette smoke and car exhaust, rapidly enters the bloodstream, firmly attaching itself to the red blood cells and preventing the uptake of oxygen. This causes the fetal haemoglobin to be artificially elevated. Carbon monoxide diffuses across the placenta, reaching levels in the fetus that may exceed the mother’s by 10 to 15%. Studies show that babies of smokers have monoxide levels that lead to approximately a 20% reduction in their blood levels of oxygen. Cases of birth defects and brain damage have been noted in laboratory animals when carbon monoxide levels are extremely high. It is felt that humans must be exposed to very high levels before these effects would occur; however, there is no known safe limit of carbon monoxide exposure.
Nicotine causes blood vessels to constrict, contributing to hypertension. The body elevates the blood pressure and the heart beats faster in an effort to counteract the loss of blood volume. This, combined with the decrease in oxygen carrying capacity of the red cells, can lead to mild angina pectoris (chest pain on exertion). The rapid drop in uterine and placental blood flow caused by constriction of maternal vessels causes the baby’s heart rate to rise in an effort to maintain oxygen levels. During ultrasound exams, maternal smoking has also been noted to decrease fetal breathing movements. Insufficient oxygen is dangerous for the fetus, especially during labour when the blood flow to the uterus is diminished during contractions.