© 2002 American Public Health Association
Robert S. Kahn and Robert C. Whitaker are with the Division of General and Community Pediatrics, Childrens Hospital Medical Center, Cincinnati, Ohio. Laura Certain is with the University of Washington School of Medicine, Seattle, Wash. Correspondence: Requests for reprints should be sent to Robert S. Kahn, MD, MPH, Division of General and Community Pediatrics, Childrens Hospital Medical Center, TCHRF 6549, 3333 Burnet Ave, Cincinnati, OH 45229-3039 (e-mail: robert.kahn{at}chmcc.org).
Objectives. This study examined the patterns and correlates of maternal smoking before, during, and after pregnancy. Methods. We examined socioeconomic, demographic, and clinical risk factors associated with maternal smoking in a nationally representative cohort of women (n = 8285) who were surveyed 17 ± 5 months and again 35 ± 5 months after delivery. Results. Smoking rates among women with a college degree decreased 30% from before pregnancy to 35 months postpartum but did not change among the least educated women. Risk factors clustered, and a gradient linked the number of risk factors (0, 2, 4) to the percentage smoking (6%, 31%, 58%, P < .0001). Conclusions. The period of pregnancy and early parenthood is associated with worsening education-related disparities in smoking as well as substantial clustering of risk factors. These observations could influence the targeting and design of maternal smoking interventions.
Smoking poses a significant threat to womens health.1 Women are more likely to stop smoking during pregnancy than at other times,1 yet the majority who quit are smoking again within 1 year postpartum.28 The lack of sustained benefit from interventions during pregnancy and postpartum916 suggests that our understanding of the determinants of smoking before, during, and after pregnancy remains inadequate. In the only national population-based longitudinal study to examine this issue, Fingerhut et al.2 found that although 39% of smokers quit during pregnancy, 70% of them relapsed within 1 year postpartum. The lowest quitting rates were among those who smoked most before pregnancy and who had the least education. No significant risk factors for smoking relapse were identified. Although this was an important early contribution to smoking cessation research, the study included only White women, had a small sample size for examining relapse rates (n = 191 quitters), and did not assess potentially important risk factors, such as income17 and the presence of other household smokers.3,57,18 A population-based, cross-sectional study found similar quitting and relapse rates but also identified African American race, parity, stressful events, and pregnancy weight gain as predictors.8 Other studies have found additional significant factors, including marital status,19 alcohol use,12 and breastfeeding.3,4 Surprisingly few studies have examined maternal depression despite the link between depression and smoking outside the context of pregnancy2026 and its prevalence among women with young children.27,28 This prior research offers a detailed but fragmented picture of the factors associated with maternal smoking. First, the relative importance of any given risk factor is difficult to interpret, because past studies each examined different sets of covariates. Second, important clinical (e.g., depressive symptoms) and social (e.g., income) risk factors remain inadequately studied. Third, no study has examined the clustering of these risk factors or assessed their cumulative effects.2931 Finally, small sample sizes,3,57 sample homogeneity,2 and a lack of longitudinal data17 have further limited interpretation. The present study used data from the 1988 National Maternal and Infant Health Survey (NMIHS) and 1991 Longitudinal Follow-Up (LF), a national cohort study designed to identify factors related to poor pregnancy outcomes.32,33 We investigated factors associated with maternal smoking trends over the course of pregnancy and the first 3 years postpartum. We examined a more comprehensive set of clinical and social factors than has been analyzed to date, for both their individual and their cumulative associations with maternal smoking behaviors.
Sample The 1988 NMIHS was a population-based survey of 9953 women giving birth in 1988. Sampling was based on birth certificates from 48 states and the District of Columbia; Black mothers and the mothers of low- and very low birthweight infants were oversampled. The 1988 NMIHS was administered 17 ± 5 months after delivery, and questions about pregnancy behaviors were based on maternal recall. The 1991 LF was administered 35 ± 5 months after delivery. Eighty-eight percent (n = 8285) of the women completed the LF, and these women constitute the sample for this study. Additional information on the NMIHS has been published elsewhere.34,35
Measures
Socioeconomic and demographic variables.
Maternal education (< 12 years, 12 years, 13 to 15 years,
Clinical variables.
Additional self-report measures from the 1988 NMIHS included amount smoked during the 3 months before conception (< 1,
We used any intention to breastfeed as a predictor for quitting during pregnancy, and ever breastfeeding as a predictor for smoking relapse after pregnancy.4 Maternal weight gain during pregnancy was constructed from the self-report of maternal weight before pregnancy and before delivery and was coded as either in the top quartile (
Contextual variables.
The number of smokers (0,
Analysis
We weighted analyses to reflect US women who had a live birth in 1988, using data provided by the National Center for Health Statistics. We used SAS Version 8.1 (SAS Institute Inc, Cary, NC) and SAS-callable SUDAAN Version 7.5.4A (Research Triangle Institute, Research Triangle Park, NC).
Twenty-nine percent of the women smoked during the 12 months before delivery, 56% quit smoking for at least 1 week during pregnancy, and the majority (72%) of women who quit were smoking again at 17 ± 5 months postpartum (Figure 1
Smoking During the 12 Months Before Delivery
Quitting During Pregnancy Women who had not completed high school were one third as likely to quit smoking during pregnancy compared with women who had graduated from college, after adjusting for covariates (Table 2
Relapsing After Pregnancy Women who lived with another smoker were 4 times as likely to relapse as women who did not live with another smoker (Table 3
Summary of Predictors Maternal education and household smoking had significant adverse associations with all three outcomes (Table 4
Depressive Symptoms and Maternal Smoking Twenty-four percent of women screened positive for depression at 17 ± 5 months postpartum. Depressive symptoms were significantly associated with concurrent smoking (odds ratio [OR] = 1.2; 95% confidence interval [CI] = 1.0, 1.4). However, they were not associated with any change in smoking status between 17 ± 5 and 35 ± 5 months (the 1988 NMIHS and 1991 LF). Among women who were not smoking at 17 ± 5 months (n = 5746), depressive symptoms at that time did not predict smoking initiation (n = 307) between the 2 surveys (OR = 0.9; 95% CI = 0.6, 1.4). Similarly, among women who were smoking at 17 ± 5 months, depressive symptoms were not associated with continued smoking between the 2 surveys (OR = 1.1; 95% CI = 0.8, 1.7).
Disparities in Smoking Over Time and Across Risk Factors
We examined the clustering of 5 risk factors found to be independently associated with current smoking at the time of the 1988 NMIHS. The risk factors were low income (< $20,000/year), less education (
Using a national sample with comprehensive demographic and clinical data, this study offers the fullest accounting to date of the patterns and correlates of smoking before, during, and after pregnancy. Three central findings emerge from this study relating to (1) the salient independent predictors of smoking outcomes, (2) the surprising lack of association between depressive symptoms and a change in smoking status, and (3) the disparities in smoking rates over time and across risk factors.
Predictors of Smoking Outcomes A strong relationship was confirmed between the presence of other household smokers and an increased risk of postpartum relapse. The effect of partner smoking has been documented in prior studies,3,57,12,15,18 and the more complete accounting for covariates in this study made little difference to the estimated effect. Studies in the general adult population have shown that such contextual smoking cues produce a desire to smoke.37 Recent animal research and human neuroimaging studies of addiction have suggested that the contextual cues themselves become directly associated with powerful neurobiological responses.38,39 The association of household smokers with postpartum relapse stands in some contrast to the weaker association of household smokers with quitting. It is not surprising that factors uniquely related to quitting may play a moderating role. For example, other smokers support for the womans quitting during pregnancy is likely stronger than their support for relapse prevention after delivery.5,18 Intervention research directed at changing the behavior of other household smokers appears to be an important area for future work. Neither parity nor birthweight was associated with protective effects. Presumably, multiparous mothers have had increased contact with health providers and therefore an increased "dose" of health education about smoking. However, consistent with Cnattingius and Thorslunds results,19 increased parity was associated with a lower rate of quitting. Perhaps a third factor, such as a womans attitude of diminished investment toward her own reproductive health and toward the health of the fetus, increases parity and reduces quitting. However, controlling for unintended pregnancy had no effect in the model of quitting. Women who have previously delivered a healthy infant despite smoking may also be less motivated to quit in subsequent pregnancies. Having a low-birthweight infant did not protect against relapse, despite presumed contact with physicians after the pregnancy. One difficulty may lie in the relative elevation of prenatal quitting messages over messages that emphasize the risk associated with smoking outside the context of pregnancy. Women who deliver low-birthweight infants despite quitting (for at least a week) may have been given little reason to "stay quit" after pregnancy. The stress of caring for a low-birthweight baby may also promote relapse. Alternatively, women with a low-birthweight infant may be more inclined to overreport having quit during pregnancy; thus, these women would appear to have higher relapse rates. In contrast to other studies, this study did not find that postpartum breastfeeding4 protected against postpartum relapse and did not find that excessive pregnancy weight gain8 had an adverse effect on postpartum relapse. Controlling for a larger number of covariates in our analyses (e.g., including other household smokers) may in part explain the different findings.
Lack of Association Between Depressive Symptoms and Change in Postpartum Smoking Status
Disparities in Smoking Over Time and Across Risk Factors Our findings support the prior literature in delineating a series of independent risk factors associated with maternal smoking. However, the results also demonstrate that these "independent" risk factors cluster together. This clustering suggests the need for a more comprehensive and integrated approach across womens many health care contacts. It may also suggest the need for a broader notion of "well-womens care" with the goal of maintaining the positive health trajectory achieved during pregnancy. Specifically, the clustering of risk factors suggests that new interventions may be required for long-term success. This may include, for example, removing financial barriers to nicotine replacement therapy, focusing on the treatment of comorbid depression or alcohol problems, and changing the behavior of other household smokers. Several limitations of this study exist. All smoking behaviors were by maternal selfreport, and behaviors during pregnancy were recalled approximately 17 months after delivery. Social desirability might lead to a biased recall of smoking. For example, underreporting of smoking might be more pronounced among highly educated women or women who had relapsed. However, self-reported smoking status, even well after the pregnancy, is reasonably accurate,4951 and less educated women may actually be more likely to underreport smoking.52 Another limitation is that the outcomes lack detail. We cannot ascertain in which trimester the women quit smoking, whether the women did not smoke for the remainder of the pregnancy, and indeed whether some women quit before conception. The reported associations are not necessarily causal. An unobserved factor, such as a capacity to delay gratification, may jointly determine both the amount of education and smoking behavior.53 It is also important to note that the prevalence of smoking among pregnant women has decreased substantially since 1988. Nevertheless, the current social patterning of smoking may be as great, if not greater, than in 1988.54 Finally, the 88% response rate for the 1991 LF may bias the findings (e.g., relating to depressive symptoms), although the direction of the potential bias is unclear. We used a nationally representative longitudinal cohort to examine the risk factors associated with smoking and relapse during the window of pregnancy and early parenthood. Of particular note was the powerful relationship between other household smokers and maternal relapse. In addition, we found that education-related disparities in smoking grew over a time period relatively rich in health care contacts and that the disparities rose sharply with an increasing number of clinical and social risk factors. Comprehensive interventions are needed that promote integration across health care contacts and that address the co-occurring morbidity that may constrain womens efforts to quit.
R. S. Kahn conceived of the study, designed and assisted in the analysis, and wrote the article. L. Certain assisted in the design and analysis and cowrote the article. R. C. Whitaker assisted in the conception of the study, interpretation of the results, and editing of the article. Accepted for publication March 10, 2002.
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