Some women keep smoking through pregnancy just because they want to give birth to a smaller baby, according to British researchers.
Even though most women now understand there is “overwhelming evidence” that smoking during pregnancy is harmful to the developing child, they continue to do so, said Professor Nick Macklon of Southampton University.
He told the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Stockholm: “It is important that people who believe that a smaller baby means an easier birth take into account the increased risk of complicated deliveries in smokers, as well as the risk of disease later in life which goes with low birth weight.”
"Smoking during pregnancy is not just bad for the mother and baby, but for the adult it ill grow into."
He and a team at the university’s department of obstetrics and gynaecology have now produced what he called the first “hard evidence” that women who stopped smoking upon discovery they were pregnant, could protect their unborn children from harm.
The study looked at over 50,000 pregnancies in the Southampton area, analysing the birth weight of the babies and comparing this to self-reported smoking behaviour.
Those who continued to smoke through pregnancy had lower weight babies.
The more women smoked the lighter their babies were: those who smoked more than 10 a day had babies weighing some 11oz (300g) less than the average birth weight from a non-smoking mother, of about 7lb 10oz (3.45kg).
However, those who ceased smoking at about the time they conceived were just as likely to give birth to a normal weight baby as those who had never smoked.
He said: “We can now give couples hard evidence that making the effort to stop smoking in the periconceptional will be beneficial for their baby.
“Stopping smoking can ameliorate these detrimental effects.”
This could help change behaviour among smoking mothers, which he said had hardly changed in Britain over the last decade.
Prof Macklon explained that smoking during pregnancy “affects the transportation of nutrients, especially oxygen, across the placenta”.
It was also “reasonable to assume” that some of the 4,000 or so toxins in cigarettes were harmful to foetuses.