Are psychosocial smoking cessation interventions delivered in pregnancy equally effective? A systematic review, meta-analysis and equity analysis of moderation analyses in randomized controlled trials

Rates of smoking in pregnancy have declined in most high-income countries. However, disparities between those of different socioeconomic statuses and ethnicities persist. We undertook this review to assess the effectiveness of interventions tailored to these equity-relevant characteristics on prenatal smoking cessation, postnatal abstinence and infant birth outcomes, and to assess whether outcomes are moderated by equity-relevant characteristics in universal interventions. We searched four databases and used supplementary search methods to identify randomized controlled trials of psychosocial smoking cessation interventions (including relapse prevention) delivered in pregnancy in high-income countries. We performed pairwise meta-analyses using robust variance estimation on tailored interventions and performed meta-regressions to test sensitivity to the proportion of minoritized ethnic participants in the trial sample. We analysed moderation of intervention effectiveness in universal interventions using harvest plots. We included 54 trials. Pairwise meta-analyses suggest intervention effectiveness for smoking cessation in pregnancy (OR 1.55, 95% CI 1.26, 1.91) and continued postnatal abstinence (OR 1.42 95% CI 1.19, 1.70). However, they did not suggest effectiveness for infant birth outcomes. In meta-regressions, effectiveness was moderated by the proportion of minoritized ethnic participants. Overall, prenatal smoking cessation and postnatal abstinence were not moderated by equity relevant characteristics in universal interventions. A reliance on universal interventions may be insufficient to positively affect existing disparities in smoking rates in pregnancy. Interventions that focus on addressing barriers to cessation related to material and financial deprivation may fail to account for broader sociocultural factors that are important to support minoritized ethnic groups.