Pregnant smokers reduced their smoking by an average of one cigarette per day before becoming aware they were pregnant, according to a new study in in Addiction Biology. In the month after learning of their pregnancy, participants reduced smoking by another four cigarettes per day.
“Our findings suggest that pregnancy could curb smokers’ desire to smoke before they are even aware of having conceived,” said the study’s lead author and principal investigator, Dr Suena Huang Massey, associate professor of psychiatry and behavioural sciences and medical social sciences at Northwestern University Feinberg School of Medicine.
“While recognition of pregnancy is a common motivation to reduce or quit smoking, if biological processes in early pregnancy are also involved as suggested by this study, identifying precisely what these processes are can lead to the development of new smoking-cessation medications.”
The vast majority of research in this field focuses on the impact of a person’s smoking on the pregnancy and the baby. This study examines, instead, the impact of pregnancy on a person’s smoking behaviour.
Though it is well known that smoking is reduced in pregnancy, it was not known when it started and whether the smokers knew they were pregnant.
“Before this paper, it was largely assumed that the only thing causing pregnant smokers to cut down was a desire to protect the baby,” Dr Massey said. “While our study does support the discovery of pregnancy as a salient event, levels of pregnancy smoking began to decline before smokers suspected they were pregnant.”
These findings support a new line of research into what happens biologically during pregnancy that might be interrupting addictive behaviours, Massey said. Her hope is that the answer to this question will lead to the discovery of new and improved ways to treat addiction.
Pregnancy hormones a contributing factor?
Human chorionic gonadotropin (hCG) is a hormone produced by the placenta in early pregnancy that is linked to morning sickness (nausea and vomiting during pregnancy).
“Strikingly, we observed the steepest declines in smoking precisely when hCG levels typically peak – between five and 10 weeks of pregnancy,” Massey said. “What’s more, pregnant smokers who do not quit during the first trimester (when hCG levels are elevated) are unlikely to quit before delivery, even with assistance from medications or financial incentives.”
Study methodology
Scientists estimated changes in cigarettes per day smoked, reported retrospectively, by 416 participants from two independent cohorts (145 from 2000 to 2005 and 271 from 2006 to 2009). Every participant was a smoker prior to becoming pregnant. Women in the study were interviewed about their smoking habits at 16 weeks of pregnancy and provided urine samples, so researchers could verify their reports.
On average, participants smoked about 10 cigarettes per day before conception. Between conception and the date they realised they were pregnant (highly variable and reported by each participant), smoking fell by an average of one cigarette per day. In the month after recognising the pregnancy, smoking dropped from an average of 9 cigarettes per day to five. Importantly, these declines were seen whether pregnancies were planned or unplanned, and whether smokers quit or did not quit.
Source: Northwestern University
