Almost half of mothers who quit smoking while pregnant resume the habit after they have given birth, research suggests.
Of 512 mothers who took part in the study, 47% resumed smoking within six weeks of delivery, according to the study published in Nicotine and Tobacco Research.
More needs to be done to reduce the number, the authors said.
Mothers living with another smoker were six times more likely to take up smoking again, the paper suggests.
Researchers, who examined data from the child health surveillance system across the UK, also found that women who resume smoking are more likely to be living in deprived urban areas, have two or more children and not have breastfed their babies.
Dr Anjum Memon, senior lecturer in public health at the Brighton and Sussex Medical School, run jointly by Brighton and Sussex universities, said: “Preventing smoking relapse is an important public health issue because of the serious health consequences for mother and child.
“This research shows that women who are most vulnerable to relapse can be identified in the antenatal period as requiring extra support or counselling after the delivery to maintain a smoke-free status.
“While designing smoking cessation counselling and or intervention services for pregnant women, it is important to take account of and involve other smokers in the household, to highlight their crucial role and support for the expectant mother in quitting and maintaining smoke-free status during the pregnancy and preventing relapse after delivery.
“These interventions may be more effective if they include strategies aimed at assisting other household members to give up smoking as well.”
Dr Diana Grice, director of public health for East Sussex, said: “It is clear that there is more that we can and should do to protect the health of pregnant women and their children.
“Stopping smoking is one of the best things anyone can do to improve their health.
“This important research provides crucial insight into the factors which influence smoking during and after pregnancy and informs the actions all services can take to improve the health of pregnant women and their families.”