Tobacco smoke contains poisonous chemicals that are carried in your bloodstream to the baby growing in your womb. These chemicals slow the growth of your baby and increase the chance of miscarriage, premature birth and stillbirth. Low birth weight is the most important reason why babies sometimes die in the first few weeks of life. If you stop smoking in the first 3 or 4 months of pregnancy your baby is likely to weigh just as much as a non-smoker's baby. In the first four months of pregnancy the baby is developing all the major organs and is very susceptible to damage from poisons like carbon monoxide in cigarette smoke.
Babies born to mothers who smoke tend to feel less well and be less contented.
In effect a smoker's baby starts life by having to give up smoking and this can make them irritable. The baby's risk of cot death increases if parents smoke. Babies born to mothers who smoke are more likely to suffer from diseases such as asthma and glue ear as children. There is increasing evidence that babies who do not grow well in the womb are more likely to develop high blood pressure, strokes and heart attacks as adults. By smoking in pregnancy you are putting your baby at risk of illnesses not just in the first few days after birth but probably for the rest of their lives.