This is a psychological fact that people start smoking during stress to seek gratification. The study done in University of East Anglia also found that mothers, who quit smoking during pregnancy, are more likely to start it again after baby is born if they feel stressed.
Supportive partners help them to stay away from smoking. Researchers studied the interview of more than 1000 new mothers and found that stress of dealing with new born baby likely to cause smoking habits in them again.
Even many women repeatedly reported that cravings for nicotine which has stopped during pregnancy return again once they give birth to a child.
