As discussed in Why Labour Hurts 2, the hard working uterus needs a good supply of oxygen whilst contracting so as not to produce lactic acid which causes pain. If you are a smoker, then every time you have a cigarette your red blood cells are filled with carbon monoxide and are unable to carry a normal amount of oxygen. This means that you have a lot less oxygen available to your baby and, if in labour, to your hard working uterus whilst smoking a cigarette. This oxygen deprivation lasts for about an hour after finishing a cigarette.
Once you are aware that smoking can cause you to have a painful labour you can take steps to remedy the situation. During your pregnancy or for at least a few weeks before you are due to go into labour you could ask your family doctor to prescribe you some nicotine patches suitable for pregnancy. They will satisfy your craving whilst making sure the oxygen carrying capacity of your blood remains at an optimal level. See your community midwife or GP for advice on who to contact about giving up smoking.
As an ex smoker I understand how difficult it is to give up. Now, as a non-smoker, I am so glad I did.
Pain Free Labour books are now available from Amazon.