Summary

Smoking during pregnancy has been linked to numerous adverse health consequences for both the developing fetus and mother. We estimated the prevalence of smoking during pregnancy by country, WHO region, and globally and the proportion of pregnant women who smoked during pregnancy, by frequency and quantity, on a global level.

For this systematic review and meta-analysis, we did a comprehensive systematic literature search for studies reporting the prevalence of smoking during pregnancy in the general population, published between Jan 1, 1985 and Feb 1, 2016, using several electronic bibliographic databases (CINAHL, Embase, ERIC, Medline, Medline in process, PsychINFO, Scopus, and Web of Science), without language or geographical restrictions. We included original research studies published in a peer-reviewed journal and assessed study quality using a tool specifically developed for use in systematic reviews addressing questions of prevalence. Studies were excluded if they did not include lifetime non-smokers in their sample or estimate, used a sample not generalisable to the general population of the respective country, or did not provide primary data. To estimate the prevalence by country, we did country-specific random-effects meta-analyses for countries with two or more available empirical studies, and we predicted the prevalence using a multilevel fractional response regression model with country-specific indicators for countries with one or no study. We estimated the proportion of female daily smokers who do not quit once pregnant by calculating the regional and global averages of the prevalence of daily smoking during pregnancy and of the prevalence of daily smoking in women. To estimate the global prevalence, by frequency and quantity, we did random-effects meta-analyses using available data from all countries and applied the respective proportions to the global prevalence estimate. We did a time–trend analysis using a univariate multilevel fractional response model. The review protocol is available on PROSPERO, registration number CRD42017075837.

Of 21 329 studies identified, 295 were retained for data extraction. We calculated estimates via meta-analysis for 43 countries and via statistical modelling for 131 countries. The three countries with the highest estimated prevalence of smoking during pregnancy were Ireland (38·4%, 95% CI 25·4–52·4), Uruguay (29·7%, 16·6–44·8), and Bulgaria (29·4%, 26·6–32·2). The global prevalence of smoking during pregnancy was estimated to be 1·7% (95% CI 0·0–4·5). The prevalence of smoking during pregnancy was 8·1% (95% CI 4·0–12·2) in the European Region, 5·9% (3·2–8·6) in the Region of the Americas, 1·2% (0·7–1·7) in the Southeast Asian Region, 1·2% (0·0–3·7) in the Western Pacific Region, 0·9% (0·0–1·9) in the Eastern Mediterranean Region, and 0·8% (0·0–2·2) in the African Region. Globally, 72·5% (95% CI 70·4–75·0) of pregnant women who smoked were daily smokers, and 27·5% (25·4–29·6) of them were occasional smokers; 51·8% (95% CI 50·0–53·5) women who smoked were light smokers, 34·8% (33·1–36·4) were moderate smokers, and 13·5% (12·3–14·7) were heavy smokers. Furthermore, the proportion of women who smoked daily and continued to smoke daily during pregnancy was 52·9% (95% CI 45·6–60·3), ranging from 30·6% (95% CI 25·6–36·4) in the European Region to 79·6% (44·2–100·0) in the Western Pacific Region.

Smoking during pregnancy is still a prevalent behaviour in many countries. These findings should inform smoking prevention programmes and health promotion strategies, as well as draw attention to the need for improved access to smoking cessation programmes for pregnant women.

Centre for Addiction and Mental Health.