Smoking behaviour in pregnancy and its impact on smoking cessation at various intervals during follow-up over 21 years: a prospective cohort study

Prevalence of smoking during pregnancy and associated social inequalities in developed countries over the 1995-2020 period: A systematic review

BACKGROUND

Smoking during pregnancy (SDP) is an important source of preventable morbidity and mortality for both mother and child.

OBJECTIVES

The aim of this study was to describe changes in the prevalence of SDP over the last 25 years in developed countries (Human Development Index >0.8 in 2020) and associated social inequalities.

DATA SOURCES

A systematic review was conducted based on a search in PubMed, Embase and PsycInfo databases and government sources.

STUDY SELECTION AND DATA EXTRACTION

Published studies between January 1995 and March 2020, for which the primary outcome was to assess the national prevalence of SDP and the secondary outcome was to describe related socio-economic data were included in the analysis. The selected articles had to be written in English, Spanish, French or Italian.

SYNTHESIS

The articles were selected after successive reading of the titles, abstracts and full-length text. An independent double reading with intervention of a third reader in case of disagreement allowed including 35 articles from 14 countries in the analysis.

RESULTS

The prevalence of SDP differed across the countries studied despite comparable levels of development. After 2015, the prevalence of SDP ranged between 4.2% in Sweden and 16.6% in France. It was associated with socio-economic factors. The prevalence of SDP slowly decreased over time, but this overall trend masked inequalities within populations. In Canada, France and the United States, the prevalence decreased more rapidly in women of higher socio-economic status, and inequalities in maternal smoking were more marked in these countries. In the other countries, inequalities tended to decrease but remained significant.

CONCLUSIONS

During pregnancy, that is a period described as a window of opportunity, smoking and social vulnerability factors need to be detected to implement targeted prevention strategies aiming at reducing related social inequalities.

Tobacco consumption from the 1st trimester of pregnancy to 7 months postpartum: Effects of previous tobacco consumption, and depression and anxiety symptoms

OBJECTIVE

Previous tobacco consumption, and depression and anxiety symptoms are major predictors of women's tobacco consumption during pregnancy and the postpartum period. However, the joint effect of these predictors is still unexplored. This study aimed to analyse the effects of previous tobacco consumption, and depression and anxiety symptoms on women's tobacco consumption status and quantity from the 1st trimester of pregnancy to 7 months postpartum.

METHOD

A sample of 803 Spanish women was assessed at the 1st and the 3rd trimester of pregnancy, and at 2 and 7 months postpartum. Previous tobacco consumption, and depression and anxiety symptoms were self-reported. Pregnancy and postpartum tobacco consumption were confirmed with biochemical tests.

RESULTS

Women with more previous tobacco consumption or more anxiety symptoms presented a steeper decrease in the number of cigarettes smoked per week from the 1st trimester of pregnancy to the childbirth, although smoking more cigarettes than women with less previous tobacco consumption or less anxiety symptoms. Women with more depression symptoms showed a higher tendency to relapse smoking during the first 2 months postpartum.

CONCLUSIONS

Previous tobacco consumption and anxiety symptoms were associated with higher smoking quantity during pregnancy, while depression symptoms were associated with consumption relapse during postpartum period.

Evaluation of a Postpartum Cardiovascular Risk Screening Clinic: An Analysis of Interpregnancy and Subsequent Pregnancy Outcomes

OBJECTIVE

At the Maternal Health Clinic (MHC), women with certain pregnancy complications are seen for appointments focusing on lifestyle modification and future pregnancy counselling. This study's objective is to determine whether women who attended the MHC following a pregnancy complicated by gestational diabetes mellitus (GDM) or a hypertensive disorder of pregnancy (HDP) have improved interpregnancy and subsequent pregnancy outcomes, compared with non-attendees.

METHODS

A retrospective cohort study was conducted including all pregnancies ≥20 weeks gestation at Kingston Health Sciences Centre (KHSC) from April 2010 to Dec 2019. Women with ≥2 deliveries were eligible for inclusion, with 2 pregnancies per woman included. These criteria identified 178 patients who attended the MHC and 133 who did not. Continuous variables with normal distribution were assessed with independent sample t tests. Continuous variables without normal distribution and ordinal variables were assessed with Mann-Whitney U tests. Categorical variables were assessed with Pearson's χ² tests. Preterm delivery, HDP and GDM recurrence, HDP and GDM progression, and change in first-trimester blood pressure and pre-pregnancy weight were examined using multivariate regression modelling. Probability values <0.05 determined significance.

RESULTS

MHC attendance was associated with improvements in interpregnancy weight reduction (P = 0.002), fewer interpregnancy type II diabetes diagnoses (P < 0.001), and a later gestational age at delivery (P < 0.001). There were no differences in subsequent pregnancy complication recurrence rates of GDM (P = 0.731) or an HDP (P = 0.139) between cohorts.

CONCLUSION

In our examination of MHC outcomes, we found improvements in certain interpregnancy and subsequent pregnancy outcomes. These results support the continued development and funding of these clinics.

Protective factors against tobacco and alcohol use among pregnant women from a tribal nation in the Central United States

Identifying social determinants of tobacco and alcohol use during pregnancy is critical to improving health outcomes for the next generation. This is especially important on a rural Tribal Nation where influences such as isolation, cultural barriers, and historical trauma have made it uniquely challenging to prevent substance use during pregnancy. The purpose of this study is to identify population-specific factors that are protective against smoking and drinking during pregnancy. We used data from 421 pregnancies collected as a part of the Safe Passages study from a rural Tribal Nation in the central United States. Pregnant women were classified as women who did not smoke (n = 84), women who quit during pregnancy (n = 23), women who smoked during pregnancy (n = 314), and women who both smoked and drank alcohol during pregnancy (n = 149). Demographic data revealed that 28.8% of the mothers were currently employed, and 91.8% of mothers reported a household income of less than $3,000 per year. Substance use rates were higher than national averages: 74.6% smoked during pregnancy and 35.4% of the women both smoked and drank alcohol during pregnancy. Five factors were identified as being protective against substance use during pregnancy: 1) living with someone (81% less likely to smoke and 92% less likely to smoke and drink), 2) having at least 12 years of education (128% less likely to smoke, and 126% less likely to smoke and drink), 3) having over 12 years of education (235% less likely to smoke, and 206% less likely to smoke and drink), 4) being employed (158% less likely to smoke, and 111% less likely to smoke and drink), and 5) not being depressed (214% less likely to smoke, and 229% less likely to smoke and drink). These social determinants should be considered for intervention research to decrease rates of substance use during pregnancy.

Factors across the life course predict women's change in smoking behaviour during pregnancy and in midlife: results from the National Child Development Study

BACKGROUND

Tobacco smoking before, during and after pregnancy remains one of the few preventable factors associated with poor health outcomes for mothers and their children. We investigate predictors across the life course for change in smoking behaviour during pregnancy and whether this change predicts smoking status in midlife.

METHODS

Data were from the National Child Development Study (1958 British birth cohort). We included female cohort members who reported a first pregnancy up to age 33 years. Among 1468 women who smoked before pregnancy, we examined predictors reported in childhood (age 11 years), adolescence (age 16 years) and early adulthood (age 23 years) of change in smoking behaviour from 12 months before to during pregnancy using log-binomial regression. The association between change in smoking behaviour during pregnancy and smoking status in midlife (age 55 years) was examined while adjusting for predictors across the life course.

RESULTS

Among prepregnancy smokers (39%), 26% reduced and 35% quit smoking during pregnancy. Parental smoking and lower social class during childhood, and early adulthood lower social class, depression, early smoking initiation, high smoking intensity, living with a smoker, no pregnancy planning and early motherhood were associated with lower probability of smoking reduction or cessation in pregnancy. Compared with women who smoked before and during pregnancy, women who reduced or quit were two times more likely to be non-smoker at age 55 years (95% CI 1.76 to 2.20).

CONCLUSIONS

Findings from this population-based birth cohort study lend support for smoking cessation strategies that target those at risk at various stages across the life course.

Psychosocial interventions for supporting women to stop smoking in pregnancy

BACKGROUND

Tobacco smoking remains one of the few preventable factors associated with complications in pregnancy, and has serious long-term implications for women and babies. Smoking in pregnancy is decreasing in high-income countries, but is strongly associated with poverty and is increasing in low- to middle-income countries.

OBJECTIVES

To assess the effects of smoking cessation interventions during pregnancy on smoking behaviour and perinatal health outcomes.

SEARCH METHODS

In this sixth update, we searched the Cochrane Pregnancy and Childbirth Group's Trials Register (13 November 2015), checked reference lists of retrieved studies and contacted trial authors.

SELECTION CRITERIA

Randomised controlled trials, cluster-randomised trials, and quasi-randomised controlled trials of psychosocial smoking cessation interventions during pregnancy.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and trial quality, and extracted data. Direct comparisons were conducted in RevMan, with meta-regression conducted in STATA 14.

MAIN RESULTS

The overall quality of evidence was moderate to high, with reductions in confidence due to imprecision and heterogeneity for some outcomes. One hundred and two trials with 120 intervention arms (studies) were included, with 88 trials (involving over 28,000 women) providing data on smoking abstinence in late pregnancy. Interventions were categorised as counselling, health education, feedback, incentives, social support, exercise and dissemination.In separate comparisons, there is high-quality evidence that counselling increased smoking cessation in late pregnancy compared with usual care (30 studies; average risk ratio (RR) 1.44, 95% confidence interval (CI) 1.19 to 1.73) and less intensive interventions (18 studies; average RR 1.25, 95% CI 1.07 to 1.47). There was uncertainty whether counselling increased the chance of smoking cessation when provided as one component of a broader maternal health intervention or comparing one type of counselling with another. In studies comparing counselling and usual care (largest comparison), it was unclear whether interventions prevented smoking relapse among women who had stopped smoking spontaneously in early pregnancy. However, a clear effect was seen in smoking abstinence at zero to five months postpartum (11 studies; average RR 1.59, 95% CI 1.26 to 2.01) and 12 to 17 months (two studies, average RR 2.20, 95% CI 1.23 to 3.96), with a borderline effect at six to 11 months (six studies; average RR 1.33, 95% CI 1.00 to 1.77). In other comparisons, the effect was unclear for most secondary outcomes, but sample sizes were small.Evidence suggests a borderline effect of health education compared with usual care (five studies; average RR 1.59, 95% CI 0.99 to 2.55), but the quality was downgraded to moderate as the effect was unclear when compared with less intensive interventions (four studies; average RR 1.20, 95% CI 0.85 to 1.70), alternative interventions (one study; RR 1.88, 95% CI 0.19 to 18.60), or when smoking cessation health education was provided as one component of a broader maternal health intervention.There was evidence feedback increased smoking cessation when compared with usual care and provided in conjunction with other strategies, such as counselling (average RR 4.39, 95% CI 1.89 to 10.21), but the confidence in the quality of evidence was downgraded to moderate as this was based on only two studies and the effect was uncertain when feedback was compared to less intensive interventions (three studies; average RR 1.29, 95% CI 0.75 to 2.20).High-quality evidence suggests incentive-based interventions are effective when compared with an alternative (non-contingent incentive) intervention (four studies; RR 2.36, 95% CI 1.36 to 4.09). However pooled effects were not calculable for comparisons with usual care or less intensive interventions (substantial heterogeneity, I2 = 93%).High-quality evidence suggests the effect is unclear in social support interventions provided by peers (six studies; average RR 1.42, 95% CI 0.98 to 2.07), in a single trial of support provided by partners, or when social support for smoking cessation was provided as part of a broader intervention to improve maternal health.The effect was unclear in single interventions of exercise compared to usual care (RR 1.20, 95% CI 0.72 to 2.01) and dissemination of counselling (RR 1.63, 95% CI 0.62 to 4.32).Importantly, high-quality evidence from pooled results demonstrated that women who received psychosocial interventions had a 17% reduction in infants born with low birthweight, a significantly higher mean birthweight (mean difference (MD) 55.60 g, 95% CI 29.82 to 81.38 g higher) and a 22% reduction in neonatal intensive care admissions. However the difference in preterm births and stillbirths was unclear. There did not appear to be adverse psychological effects from the interventions.The intensity of support women received in both the intervention and comparison groups has increased over time, with higher-intensity interventions more likely to have higher-intensity comparisons, potentially explaining why no clear differences were seen with increasing intervention intensity in meta-regression analyses. Among meta-regression analyses: studies classified as having 'unclear' implementation and unequal baseline characteristics were less effective than other studies. There was no clear difference between trials implemented by researchers (efficacy studies), and those implemented by routine pregnancy staff (effectiveness studies), however there was uncertainty in the effectiveness of counselling in four dissemination trials where the focus on the intervention was at an organisational level. The pooled effects were similar in interventions provided for women classified as having predominantly low socio-economic status, compared to other women. The effect was significant in interventions among women from ethnic minority groups; however not among indigenous women. There were similar effect sizes in trials with biochemically validated smoking abstinence and those with self-reported abstinence. It was unclear whether incorporating use of self-help manuals or telephone support increased the effectiveness of interventions.

AUTHORS' CONCLUSIONS

Psychosocial interventions to support women to stop smoking in pregnancy can increase the proportion of women who stop smoking in late pregnancy and the proportion of infants born low birthweight. Counselling, feedback and incentives appear to be effective, however the characteristics and context of the interventions should be carefully considered. The effect of health education and social support is less clear. New trials have been published during the preparation of this review and will be included in the next update.

Re-starting smoking in the postpartum period after receiving a smoking cessation intervention: a systematic review

AIMS

In pregnant smoking cessation trial participants, to estimate (1) among women abstinent at the end of pregnancy, the proportion who re-start smoking at time-points afterwards (primary analysis) and (2) among all trial participants, the proportion smoking at the end of pregnancy and at selected time-points during the postpartum period (secondary analysis).

METHODS

Trials identified from two Cochrane reviews plus searches of Medline and EMBASE. Twenty-seven trials were included. The included trials were randomized or quasi-randomized trials of within-pregnancy cessation interventions given to smokers who reported abstinence both at end of pregnancy and at one or more defined time-points after birth. Outcomes were validated biochemically and self-reported continuous abstinence from smoking and 7-day point prevalence abstinence. The primary random-effects meta-analysis used longitudinal data to estimate mean pooled proportions of re-starting smoking; a secondary analysis used cross-sectional data to estimate the mean proportions smoking at different postpartum time-points. Subgroup analyses were performed on biochemically validated abstinence.

RESULTS

The pooled mean proportion re-starting at 6 months postpartum was 43% [95% confidence interval (CI) = 16-72%, I(2)  = 96.7%] (11 trials, 571 abstinent women). The pooled mean proportion smoking at the end of pregnancy was 87% (95% CI = 84-90%, I(2)  = 93.2%) and 94% (95% CI = 92-96%, I(2)  = 88%) at 6 months postpartum (23 trials, 9262 trial participants). Findings were similar when using biochemically validated abstinence.

CONCLUSIONS

In clinical trials of smoking cessation interventions during pregnancy only 13% are abstinent at term. Of these, 43% re-start by 6 months postpartum.

Cigarette Smoking Among Working Women of Reproductive Age-United States, 2009-2013

BACKGROUND

Employers play a vital role in promoting and supporting tobacco use cessation among tobacco-using workers. Cigarette smoking during pregnancy is a preventable cause of complications in pregnancy and adverse infant health outcomes.

PURPOSE

To estimate cigarette smoking prevalence and attempts to quit among working women of reproductive age in different industries and occupations using a nationally representative survey.

METHODS

The 2009-2013 National Health Interview Survey data for women of reproductive age (18-49 years) who were working in the week prior to the interview (n = 30855) were analyzed. Data were adjusted for nonresponse and weighted to produce nationally representative estimates.

RESULTS

During 2009-2013, among working women of reproductive age, an estimated 17.3% (95% confidence interval [CI]: 16.7-17.8) and 12.9% (95% CI: 12.4-13.4) were current and former cigarette smokers, respectively. Of women who smoke daily, 44.5% (95% CI: 42.5-46.5) had made a quit attempt for more than 1 day in the year before the interview. Cigarette smoking prevalence was highest among women working in the construction industry (29.2%; 95% CI: 22.8-35.7) and in construction and extraction occupations (34.6%; 95% CI: 23.4-45.9). Among working women who were pregnant at the time of the interview, 6.8% (95% CI: 4.4-9.2) and 20.4% (95% CI: 16.9-24.0) were current and former cigarette smokers, respectively.

CONCLUSIONS

Cigarette smoking prevalence varies by industry and occupation. Intensifying tobacco control efforts in high prevalence industries and occupations could result in higher cessation rates and improvements in health among women of reproductive age.

IMPLICATIONS

This study identified discrepancies in cigarette smoking among women of reproductive age across industries and occupations. In the absence of smoke-free local and state laws, employer-established smoke-free policies and workplace cessation programs are important for achieving reduction of tobacco use among women and for protecting other workers' health. Results in this report may assist in developing educational campaigns targeting women in industries and occupations with high prevalence of cigarette smoking and low percentage of ever-smokers who had quit.

Other adverse pregnancy outcomes and future chronic disease

Cardiovascular disease is the leading cause of morbidity and mortality in females worldwide. Pregnancy is associated with significant physiologic changes that may function as a natural stress test to detect women at future risk. It is established that women who have had a pregnancy complicated by gestational diabetes or a hypertensive disorder of pregnancy are at increased risk of cardiovascular disease later in life, and there is growing evidence that women who deliver infants preterm or growth-restricted infants have an elevated risk as well. Consideration should be given to including these outcomes as indicators of cardiovascular risk. Pregnancy represents a teachable moment when it would be ideal to identify women at risk. Improved integration of women's primary health care and an enhanced knowledge base on the part of clinicians will be necessary to fully incorporate these findings into the clinical care of women.

A critical review of smoking, cessation, relapse and emerging research in pregnancy and post-partum

INTRODUCTION

Smoking during pregnancy causes adverse health outcomes. Though the prevalence of smoking among pregnant women has declined, postpartum relapse rates remain high and smoking-related maternal, fetal and infant morbidity and mortality remains a public health burden.

SOURCES OF DATA

A comprehensive literature search on smoking in pregnancy was conducted to provide a practical review for health professionals.

AREAS OF AGREEMENT

Psychosocial support is an effective evidence-based treatment for pregnant women. Bio-psycho-socio factors that influence likelihood of quitting and remaining quit should be addressed.

AREAS OF CONTROVERSY

Electronic cigarettes are marketed as a harm reduction tool, but research on safety and effectiveness are lacking for pregnant women.

GROWING POINTS

The safety and efficacy of pharmacotherapy for use among pregnant women remains unclear. Clinicians should increase discussions regarding all resources for tobacco use treatment and secondhand smoke (SHS) exposure during pregnancy and postpartum and offer psychosocial support to all pregnant women.

AREAS TIMELY FOR DEVELOPING RESEARCH

Research on developing stronger tobacco control policies in low- and middle-income countries, increasing cessation and relapse prevention among pregnant smokers with mental health conditions and increasing the impact of evidence-based supports, such as the quitline, among pregnant women can decrease consumption of tobacco in pregnancy.

Are secondhand smoke-related diseases of children associated with parental smoking cessation? Determinants of parental smoking cessation in a population-based cohort study

OBJECTIVE

Little is known about whether secondhand smoke (SHS)-related diseases of young children, such as asthma, induce parental smoking cessation during the early child-rearing period. Our objective was therefore to show the association in addition to other potential determinants of parental cessation.

METHODS

We analyzed data from the Longitudinal Survey of Newborns in the 21st Century in Japan, from 0.5years (N=47,015) to 4.5years (N=39,817), having selected participants whose parents smoked at baseline (maternal smoking N=8,037; paternal smoking N=28,486). Multivariable log-binomial regression models were used to calculate the prevalence ratios for parental smoking cessation according to the onset of SHS-related diseases of their children, using inverse probability weight to account for non-response at follow-up.

RESULTS

A total of 16.7% of smoking mothers and 14.5% of smoking fathers had stopped smoking at follow-up. The onset of SHS-related children's diseases was not statistically significantly associated with either maternal or paternal smoking cessation after multivariable adjustments. Strong determinants were, for example, number of cigarettes smoked per day and partner's smoking status during follow-up.

CONCLUSION

SHS-related children's diseases were not associated with parental smoking cessation. It may therefore be necessary to provide additional support for parental smoking cessation within their child's medical care setting.

Can 'early programming' be partly explained by smoking? Results from a prospective, population-based cohort study

BACKGROUND

Numerous studies have focused the association between low birthweight and later disease. Our objective was to study the association between birthweight and later adult smoking and thereby explore a possible mechanism for the association between low birthweight and later adult disease.

METHODS

We studied associations between birthweight of women (n=247704) born in 1967-1995 and smoking habits at the end of their pregnancy 13-42 years later in a prospective, population-based cohort study from The Medical Birth Registry of Norway. Similarly, the association between birthweight of men (n=194393) and smoking habits of their partners were assessed. Finally, we studied the relation between smoking habits of the participating women and the cause specific death of their mothers (n=222808).

RESULTS

Twenty per cent of women with birthweight less than 2000 g were adult daily smokers compared with 11% with birthweight 4000-4499 g [relative risk=1.8, 95% confidence interval 1.4, 2.2]. Similarly, we found an association between men's birthweight and their partners smoking habits. Mothers of smoking women had doubled risk of dying from lung cancer and from cardiovascular disease compared with mothers of non-smoking women.

CONCLUSIONS

Being born with low birthweight is associated with smoking in adulthood. Associations of adult smoking with partners' birthweight and mothers' smoking-related causes of death suggest a shared smoking environment, and may account for some of the established association between birthweight and later cardiovascular disease.

Importance of engaging obstetrician/gynecologists in cardiovascular disease prevention

PURPOSE OF REVIEW

To review recent evidence regarding traditional and sex-specific factors identified among women during their reproductive years and their importance in lifetime risk for cardiovascular disease (CVD).

RECENT FINDINGS

Longitudinal studies demonstrated a woman's burden of risk during her reproductive years is associated with future risk of CVD. Similarly, women with a healthy lifestyle are relatively protected and have the lowest lifetime risk. Some primary prevention strategies, when implemented during this age window, were cost-effective. The link between pregnancy outcome and future CVD risk is now better understood, and evidence now relates pregnancy-associated hypertension and diabetes, as well as a preterm delivery or a low birth weight delivery, to excess risk. Gaps in preventive healthcare for women in this age group included low rates of treatment initiation for hypertension and failure to follow guidelines for diabetes surveillance among women with a history of gestational diabetes. Knowledge gaps for standard CVD prevention, as well as the link between pregnancy complications and future CVD risk, were identified among both primary care providers and obstetrician/gynecologists.

SUMMARY

Traditional and sex-specific risk factors for CVD present during women's reproductive years. Engaging the obstetrician/gynecologist provides a strategy to enhance prevention.

Psychosocial interventions for supporting women to stop smoking in pregnancy

BACKGROUND

Tobacco smoking in pregnancy remains one of the few preventable factors associated with complications in pregnancy, stillbirth, low birthweight and preterm birth and has serious long-term implications for women and babies. Smoking in pregnancy is decreasing in high-income countries, but is strongly associated with poverty and increasing in low- to middle-income countries.

OBJECTIVES

To assess the effects of smoking cessation interventions during pregnancy on smoking behaviour and perinatal health outcomes.

SEARCH METHODS

In this fifth update, we searched the Cochrane Pregnancy and Childbirth Group's Trials Register (1 March 2013), checked reference lists of retrieved studies and contacted trial authors to locate additional unpublished data.

SELECTION CRITERIA

Randomised controlled trials, cluster-randomised trials, randomised cross-over trials, and quasi-randomised controlled trials (with allocation by maternal birth date or hospital record number) of psychosocial smoking cessation interventions during pregnancy.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and trial quality, and extracted data. Direct comparisons were conducted in RevMan, and subgroup analyses and sensitivity analysis were conducted in SPSS.

MAIN RESULTS

Eighty-six trials were included in this updated review, with 77 trials (involving over 29,000 women) providing data on smoking abstinence in late pregnancy.In separate comparisons, counselling interventions demonstrated a significant effect compared with usual care (27 studies; average risk ratio (RR) 1.44, 95% confidence interval (CI) 1.19 to 1.75), and a borderline effect compared with less intensive interventions (16 studies; average RR 1.35, 95% CI 1.00 to 1.82). However, a significant effect was only seen in subsets where counselling was provided in conjunction with other strategies. It was unclear whether any type of counselling strategy is more effective than others (one study; RR 1.15, 95% CI 0.86 to 1.53). In studies comparing counselling and usual care (the largest comparison), it was unclear whether interventions prevented smoking relapse among women who had stopped smoking spontaneously in early pregnancy (eight studies; average RR 1.06, 95% CI 0.93 to 1.21). However, a clear effect was seen in smoking abstinence at zero to five months postpartum (10 studies; average RR 1.76, 95% CI 1.05 to 2.95), a borderline effect at six to 11 months (six studies; average RR 1.33, 95% CI 1.00 to 1.77), and a significant effect at 12 to 17 months (two studies, average RR 2.20, 95% CI 1.23 to 3.96), but not in the longer term. In other comparisons, the effect was not significantly different from the null effect for most secondary outcomes, but sample sizes were small.Incentive-based interventions had the largest effect size compared with a less intensive intervention (one study; RR 3.64, 95% CI 1.84 to 7.23) and an alternative intervention (one study; RR 4.05, 95% CI 1.48 to 11.11).Feedback interventions demonstrated a significant effect only when compared with usual care and provided in conjunction with other strategies, such as counselling (two studies; average RR 4.39, 95% CI 1.89 to 10.21), but the effect was unclear when compared with a less intensive intervention (two studies; average RR 1.19, 95% CI 0.45 to 3.12).The effect of health education was unclear when compared with usual care (three studies; average RR 1.51, 95% CI 0.64 to 3.59) or less intensive interventions (two studies; average RR 1.50, 95% CI 0.97 to 2.31).Social support interventions appeared effective when provided by peers (five studies; average RR 1.49, 95% CI 1.01 to 2.19), but the effect was unclear in a single trial of support provided by partners.The effects were mixed where the smoking interventions were provided as part of broader interventions to improve maternal health, rather than targeted smoking cessation interventions.Subgroup analyses on primary outcome for all studies showed the intensity of interventions and comparisons has increased over time, with higher intensity interventions more likely to have higher intensity comparisons. While there was no significant difference, trials where the comparison group received usual care had the largest pooled effect size (37 studies; average RR 1.34, 95% CI 1.25 to 1.44), with lower effect sizes when the comparison group received less intensive interventions (30 studies; average RR 1.20, 95% CI 1.08 to 1.31), or alternative interventions (two studies; average RR 1.26, 95% CI 0.98 to 1.53). More recent studies included in this update had a lower effect size (20 studies; average RR 1.26, 95% CI 1.00 to 1.59), I(2)= 3%, compared to those in the previous version of the review (50 studies; average RR 1.50, 95% CI 1.30 to 1.73). There were similar effect sizes in trials with biochemically validated smoking abstinence (49 studies; average RR 1.43, 95% CI 1.22 to 1.67) and those with self-reported abstinence (20 studies; average RR 1.48, 95% CI 1.17 to 1.87). There was no significant difference between trials implemented by researchers (efficacy studies), and those implemented by routine pregnancy staff (effectiveness studies), however the effect was unclear in three dissemination trials of counselling interventions where the focus on the intervention was at an organisational level (average RR 0.96, 95% CI 0.37 to 2.50). The pooled effects were similar in interventions provided for women with predominantly low socio-economic status (44 studies; average RR 1.41, 95% CI 1.19 to 1.66), compared to other women (26 studies; average RR 1.47, 95% CI 1.21 to 1.79); though the effect was unclear in interventions among women from ethnic minority groups (five studies; average RR 1.08, 95% CI 0.83 to 1.40) and aboriginal women (two studies; average RR 0.40, 95% CI 0.06 to 2.67). Importantly, pooled results demonstrated that women who received psychosocial interventions had an 18% reduction in preterm births (14 studies; average RR 0.82, 95% CI 0.70 to 0.96), and infants born with low birthweight (14 studies; average RR 0.82, 95% CI 0.71 to 0.94). There did not appear to be any adverse effects from the psychosocial interventions, and three studies measured an improvement in women's psychological wellbeing.

AUTHORS' CONCLUSIONS

Psychosocial interventions to support women to stop smoking in pregnancy can increase the proportion of women who stop smoking in late pregnancy, and reduce low birthweight and preterm births.