Smoking and experiencing depressive symptoms during pregnancy have both been linked independently to lower birth weights in infants, but little is known about the interaction between the two risk factors. A new study by Duke researchers reveals that the combination of the two can exacerbate their effects and lead to even lower birth weights.
“Rates of low birth weights have increased in the U.S., so the findings have important implications for mitigating negative perinatal outcomes for pregnant women and their children,” says Julia Schechter, PhD, a clinical psychologist and researcher in the Duke Department of Psychiatry and Behavioral Sciences and lead author of the study published in December 2018 in Nicotine & Tobacco Research. “Prenatal smoke exposure and prenatal depressive symptoms are both very common risk factors during pregnancy, so we wanted to look at their interaction.”
The researchers designed the study to overcome the shortcomings of some previous studies. For example, most studies on prenatal smoking rely on the problematic approach of self-reporting. The Duke study measured the level of cotinine in the subjects’ blood during pregnancy, a biomarker that gives objective evidence of the actual level of smoke exposure, including from second-hand smoke.
This use of a biomarker was a difference-maker: The significant interaction found between cotinine levels and depressive symptoms was not evident when self-reporting was used as the measure of smoking. This detail means that relying on self-reporting may miss some women in this vulnerable population and that some women may be exposed passively without realizing the impact on their pregnancies.
The women’s depressive symptoms were assessed via a commonly used measure of depression that asks about symptoms such as a loss of energy, increased sleepiness, difficulties concentrating, changes in eating habits, and having increased thoughts about death or dying.
The combination of smoking and depressive symptoms was associated with lower birth weights in women reporting higher levels of depressive symptoms, but not in those with lower levels. The women who were exposed to smoke, and whose symptoms were above the threshold to be considered a higher level of depressive symptoms, were more likely to have a low birth weight infant (less than 2500 g).
“The take-home message is that there appears to be a highly vulnerable population of women that providers should be aware of,” Schechter says. “The combination of smoke exposure and being depressed might put women at greater risk for having lower birth weight babies, so they should be monitored. Both smoke exposure and depression are modifiable risk factors. They are things that we can change, and that is exciting, because this research tells us that we might be able to have an effect on birth weight.”