Within-person decline in pregnancy smoking is observable prior to pregnancy awareness: Evidence across two independent observational cohorts

Abstract

Decreased consumption of nicotine and other drugs during pregnancy appears to be a cross-species phenomenon from which mechanism(s) capable of interrupting addictive processes could be elucidated. Whether pregnancy influences smoking behaviour independent of women's knowledge of the pregnancy, however, has not been considered. Using repeated measures analysis of variance (ANOVA), we estimated within-person change in mean cigarettes/day smoked across the estimated date of conception but prior to individually reported dates of pregnancy recognition using longitudinal smoking data from two independent observational cohorts, the Growing Up Healthy (GUH, n = 271) and Midwest Infant Development Studies (MIDS, n = 145). Participants smoked an average of half a pack/day in the month immediately before conception (M (SD) = 12(8.1) and 9.5(6.7) cigarettes/day in GUH and MIDS, respectively). We observed within-person declines in smoking after conception, both before (M_GUH = -0.9; 95% CI -1.6, -0.2; p = 0.01; M_MIDS = -1.1; 95% CI -1.9, -0.3; p = 0.01) and after (M_GUH = -4.8; 95% CI -5.5, -4.1; p < 0.001; M_MIDS = -3.3; 95% CI -4.4, -2.5; p < 0.001) women were aware of having conceived, even when women who had quit and women who were planning to conceive were excluded from analyses. Pregnancy may interrupt smoking-related processes via mechanisms not previously considered. Plausible candidates and directions for future research are discussed.

Keywords: gestation; nicotine; pregnancy smoking; prevention; smoking cessation.

FIGURE 1

TOP: Cross-species conservation of pregnancy's protective effect on substance use implicates mechanism(s) other than concerns about intrauterine exposure. BOTTOM: In humans, the temporal discrepancy between the onset of pregnancy (conception) and recognition of pregnancy enables inference of putative biological influences on smoking independent of psychological processes (deliberate harm reduction) occurring once the pregnancy is recognised.

FIGURE 2

Derivation of analytic samples from original cohorts

FIGURE 3

TOP: Estimated effects of pregnancy onset (conception) and pregnancy recognition on smoking, operationalised as mean within-individual change in cigarettes per day from coordinated and meta-analysis. BOTTOM: Graphical depiction of mean within-individual change in smoking by cohort

FIGURE 4

Sensitivity analyses of: (a) persistent pregnancy smokers who smoked throughout the entire pregnancy (TOP); (b) nonquitters, that is, women still smoking at each interval (n's shown along x-axis) (MIDDLE); and (c) unplanned pregnancies only (BOTTOM)