Women may not be accurately reporting how many cigarettes they smoke daily during pregnancy

Studies that report lower smoking rates during pregnancy may be flawed by the social stigma attached to mothers-to-be who light up but don’t admit it, suggests a new analysis.

Looking at previous studies and newly analyzing 67,395 pregnancies in Kansas City, Mo., in a recent 10-year period, researchers writing in the September-October American Journal of Health Behavior conclude that inaccurate self-reporting of cigarette use calls into question assumptions that there is, in fact, a reduction.

“Indeed, it is unclear whether smoking rates are decreasing or whether fewer women are accurately reporting how many cigarettes they smoke daily during pregnancy,” say the authors, led by Dr. Felix A. Okah of the University of Missouri, Kansas City.

Although pregnant women may be smoking less, “it is equally plausible that greater awareness over time of general, and especially of fetal, health consequences of smoking may make women less likely to admit to smoking and more likely to underreport the number of cigarettes smoked daily,” says Okah.

Even assuming accuracy, the drop in pregnancy smoking rates occurred only in women over age 20.

The researchers analyzed records of 67,395 live-birth pregnancies during the periods 1993–1997 and 1998–2002. The information was gathered from computer files from the Kansas City (Mo.) Health Department and from birth certificates.

The women were asked if they used tobacco during pregnancy and their average number of cigarettes per day. The researchers used “light” (1-9 cigarettes per day), “moderate” (10-19 cigarettes per day) and “heavy” (more than 19 cigarettes per day) to categorize the smokers and to observe shifts during pregnancy between categories.

The results indicate that smoking rates declined by 22 percent over the two five-year periods. However, among those who continued to smoke during pregnancy, there was a self-reported shift toward “light” smoking across educational, age and racial groups. This was suspicious, according the researchers, because other more general smoking studies suggest that light smokers are the most likely to quit and heavy smokers do not shift.

“The good news is that there is a decline in reported smokers during pregnancy,” says Norman Edelman, M.D., dean of the State University of New York School of Medicine in Stonybrook. “But smokers are notoriously poor in estimating how much they smoke, so I don’t make much of the apparent shift to light smoking,” he says.

Uncertainty about the accuracy and meaning of existing research “and the magnitude of nondisclosure of smoking during pregnancy warrant the use of more accurate measures of smoking trends if limited public health resources are to be spent judiciously,” Okah says. At the same time, tools such as urine or saliva samples “would prove exorbitant” if routinely used. Instead, he recommends intermittent random urine or saliva testing of pregnant women as a more objective measure.

Earlier research that supports such suspicion shows a nondisclosure rate as high as 32 percent among self-reported quitters.

“Cigarette smoking during pregnancy continues to be a major preventable cause of premature birth, low birth weight, and smallness for gestational age,” the researchers write.