Smoking tobacco is harmful for everyone – be it a man or a woman, old or young, the thousands of chemicals in tobacco leads to various health problems. But, smoking during pregnancy is even more harmful as it affects both the mother and the unborn child, increasing the risks of various irreversible complications and birth defects. Smoking tobacco in any form, cigarettes, cigars and even hookah, is equally bad for pregnant women.
During pregnancy, the developing fetus gets all the oxygen and nutrients it needs from the mother through the umbilical cord . There are over 4,000 harmful chemicals in cigarettes, including extremely dangerous substances like lead, cyanide  and around 60 carcinogenic compounds. As you smoke, these toxic compounds enter your bloodstream, contaminating the only source of nutrients and oxygen for the fetus.
Among all the threatening substances, carbon monoxide and nicotine are the most harmful, accounting for most of the smoking related complications in pregnancy . Nicotine narrows the blood vessels in your body, including those in the umbilical cord. This reduces the oxygen supply to the baby, requiring the under-developed heart to beat harder, the more the mother smokes . Additionally, the red blood cells (RBCs) carrying oxygen begin picking up carbon monoxide molecules instead, lowering the oxygen supply even further . The limited oxygen and nutrient supply hinder the development of various organs and body parts of your baby, leading to growth restriction and various birth defects.
Smoking should also be avoided by breastfeeding women to protect their babies from the same harmful substances .
Smoking during any stage in pregnancy is harmful for the baby, but the dangers are somewhat higher during the first weeks of fetal development . The embryo (your baby) undergoes the most crucial development during the initial months as the principal systems and organs (e.g. the neural tube, circulatory system, heart and digestive system) begin developing at this stage. So, a shortage of oxygen and nutrients at this stage may hamper the basic fetal development, leading to serious organ defects and developmental problems.
According to Robert Welch, the chairman of the Department of Obstetrics and Gynecology at Providence Hospital in Southfield, Michigan, smoking while pregnant is one of the principal causes leading to adverse outcomes in babies . Studies show around 5% of the total infant deaths to occur due to smoking during pregnancy .
Long Term Effects
Babies born to mothers who smoked during pregnancy are more likely to smoke when they grow up 
Women suffering from epilepsy should stay away from cigarettes when pregnant as it increases the risk of pre-mature labor and contractions .
Some women try to cut down the number of cigarettes they smoke everyday while others think it is safer to switch to lighter brands. Although, the less you smoke the safer it is for the baby, giving up tobacco altogether is the only way of ensuring a healthy pregnancy and baby. The harmful substances in tobacco may have considerable ill effects on the fetus even if you smoke only one cigarette a day. Here are the principal benefits of giving up smoking during pregnancy:
Secondhand or passive smoke is the mixture of the smoke coming from the burning end of a cigarette and that exhaled by a smoker . The smoke burning off the end of a cigar or cigarette contains more harmful substances than that inhaled while smoking . Researches show that women exposed to passive smoke during pregnancy have 23 percent higher chances of delivering a stillborn baby while the risks of birth defects increase by 13 percent . Regular exposure to secondhand smoke heightens the risks of the following problems both in the mother and child:
Serious consequences of passive smoke may also include low birth weight, congenital defects, SIDS and stillbirth .
If you are unable to stop smoking completely at once, try to gradually cut back the number of cigarettes you smoke every day until you do not need to smoke again. However, it is advisable to try and complete this long-term stop-smoking plan within the 14 week of pregnancy .
Scientific researches show smoking to have an adverse effect on female fertility  with studies showing infertility to be more common in women who smoke. Additionally, smokers are likely to face more difficulty in conceiving compared to non-smokers. So, it is recommended to give up tobacco as soon as you start planning to have a baby. Smoking is also known to increase the chances of having an ectopic pregnancy 
Smoking in pregnancy is not illegal in the United States. However, there is a significant amount of debate regarding whether or not it should be made illegal as it can be considered a form of child abuse.