Study links smoking during pregnancy to socioeconomic status
Women of lower socioeconomic groups more commonly smoke before, during and after pregnancy, according to a University of Queensland study.
The study, led by Anthropology and Sociology Department head Professor Jake Najman, also found that women who quit smoking during pregnancy had a more than 50 percent chance of relapsing within six months of the birth, regardless of income level.
This is the first known longitudinal study to examine the association between socioeconomic status and smoking before, during and after pregnancy. Data was taken from the Mater Hospital-University of Queensland Study of Pregnancy.
"Young, single mothers are more likely to be heavy smokers and are more likely to be poor," Professor Najman said.
He said the study showed that not only was smoking fairly common in pregnancy but occurred at a higher rate than among non-pregnant women of a similar age.
"It must be of great public health concern that more than one-third of public obstetric patients were smokers at their first clinic visit," he said.
Of the 5147 participants, 2326 (45.2 percent) reported they had smoked cigarettes before becoming pregnant. At the first clinic visit, 1759 women (34.2 percent) were smokers. Some 681 women had stopped smoking by their first clinic visit presumably because they were pregnant. Of those who had quit, 134 (19.7 percent) had previously been heavy smokers (20 or more cigarettes per day).
Socioeconomic status was measured as an average of the family income over more than five years from the first clinic visit to the five-year follow-up. Six percent of mothers (323) were in the lowest income group with a mean estimated income of $4144 per year.
In the highest income group were 10.9 percent of mothers (538) with an mean estimated income of $21,639 or more. The remaining mothers (83.1 percent or 4438) had incomes in between these amounts.
Respondents were also categorised according to the number of cigarettes smoked per day - an average of 19 a day was light/moderate while 20 or more was considered heavy.
Other researchers involved with the study were Andrea Lanyon from the Anthropology and Sociology Department, Margaret Andersen and Gail Williams from the University's Social and Preventive Medicine Department, Dr William Bor from the Enoggera Child and Youth Mental Health Service and Dr Michael O'Callaghan from the Mater Childrens' Hospital.
The study found:
o A substantial minority of women reduced their cigarette consumption or quit altogether during the first trimester of pregnancy - 21.6 percent of women in the low income group, 24.4 percent in the middle income group and 33.9 percent in the high income group.
Rates of maternal heavy smoking before pregnancy, at six months and five years after the birth were similar.
Professor Najman said this result suggested there was an association between family income and the rate at which smoking pregnant mothers stopped smoking before the first clinic visit.
"The higher the family income, the greater the likelihood of a mother stopping smoking by her first clinic visit. This result remains the same even after adjustment for the mother's age and marital status," he said.
o More than half the women in the highest income group did not smoke and few were categorised as heavy smokers while two-thirds of the women in the low income group smoked with one in four classified as a heavy smoker.
"At least part of the association between family income and smoking can be attributed to the younger age and single marital status of the most economically disadvantaged group," Professor Najman said.
o Between 50 and 55 percent of women who quit smoking when they were pregnant had relapsed within six months of giving birth regardless of income category. By this six-month stage, rates of heavy smoking returned to pre-pregnancy levels.
"Relapse rates appear to be related to three major factors: having a smoker in the immediate environment (usually the mother's partner); being a previously heavy smoker; and reporting stressful experiences in the postnatal period such as depression and boredom," Professor Najman said.
"Advertising and the manipulation of idealised female images were also believed to contribute to decisions to relapse.
"Many women who manage to give up smoking subsequently relapse. A major opportunity is being missed here - to mount maintenance programs to persuade women that they should remain free of the cigarette-smoking habit."
Professor Najman said the study's findings in relation to smoking and socioeconomic status suggested public health initiatives such as raising the cost of cigarettes would be effective in reducing smoking rates.
"The study also found that smoking is part of a broader pattern of behaviour and lifestyle. Those who smoke are more likely to drink alcohol and eat less healthy food," he said.
"Attention needs to be paid to a mother's total lifestyle rather than just to a single behaviour.
"Another major finding is that women are sufficiently concerned about the effect of smoking on their unborn child to stop or reduce their cigarette intake. There is an opportunity to build upon these concerns and persuade even more women that the health of their unborn children demands that they stop smoking.
"Evidence suggests that most pregnant women smokers want to stop. In these circumstances, it could be argued that a failure to mount stop-smoking programs for pregnant women constitutes evidence of inadequate medical care."
For more information, contact Professor Najman (telephone 07 3365 3152).
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