Tobacco use and secondhand smoke exposure during pregnancy in two African countries: Zambia and the Democratic Republic of the Congo

Authors


Michele Bloch, National Cancer Institute, Executive Plaza North, room 4038, 6130 Executive Boulevard, MSC 7337, Bethesda, MD 20892-7337, USA. E-mail: blochm@mail.nih.gov

Abstract

Objective. To study pregnant women's knowledge, attitudes and behaviors towards tobacco use and secondhand smoke (SHS) exposure, and exposure to advertising for and against tobacco products in Zambia and the Democratic Republic of the Congo (DRC). Design. Prospective cross-sectional survey between November 2004 and September 2005. Setting. Antenatal care clinics in Lusaka, Zambia, and Kinshasa, DRC. Population. Pregnant women in Zambia (909) and the DRC (847). Methods. Research staff administered a structured questionnaire to pregnant women attending antenatal care clinics. Main outcome measures. Pregnant women's use of tobacco, exposure to SHS, knowledge of the harms of tobacco and exposure to advertising for and against tobacco products. Results. Only about 10% of pregnant women reported ever having tried cigarettes (6.6% Zambia; 14.1% DRC). However, in the DRC, 41.8% of pregnant women had tried other forms of tobacco, primarily snuff. About 10% of pregnant women and young children were frequently or always exposed to SHS. Pregnant women's knowledge of the hazards of smoking and SHS exposure was extremely limited. About 13% of pregnant women had seen or heard advertising for tobacco products in the last 30 days. Conclusions. Tobacco use and SHS exposure pose serious threats to the health of women, infants and children. In many African countries, maternal and infant health outcomes are often poor and will likely worsen if maternal tobacco use increases. Our findings suggest that a ‘window of opportunity’ exists to prevent increased tobacco use and SHS exposure of pregnant women in Zambia and the DRC.

Introduction

Tobacco use is widely recognized as one of the leading threats to global health (1). While tobacco use is stable or decreasing in most high-income countries, it is increasing in many low- and middle-income countries (2). Currently, the prevalence of smoking by men in developing countries is far higher than that by women; it is estimated that about 50% of men in developing countries smoke cigarettes, compared with only 9% of women (3). However, there is evidence that the relatively low rates of tobacco use by women in the developing world could rise very quickly (4, 5).

Pregnant women are an important subpopulation to target for tobacco control efforts because both cigarettes and smokeless tobacco products pose serious risks to fetal and newborn health. Cigarette smoking during pregnancy increases the risk of premature rupture of the membranes, placenta previa, placental abruption, preterm delivery and shortened gestation, fetal growth restriction and low birth weight and sudden infant death syndrome (6). The use of smokeless tobacco during pregnancy has been associated with stillbirth, preterm birth and reduced birth weight (7–9). Maternal tobacco use is also likely to expose infants and young children to secondhand smoke (SHS), a serious health hazard, and to provide role modeling for older children's use of tobacco. Finally, pregnant women who use tobacco may be highly motivated to quit, benefiting their own health and that of their developing child (10, 11).

Sub-Saharan Africa is thought to have one of the world's lowest rates of cigarette consumption, largely attributed to low purchasing power and low rates of female tobacco use (12). However, many African countries lack reliable data on tobacco use by women, including pregnant women, which are needed to inform tobacco control and prevention efforts (13, 14). For this reason, we undertook a prospective study of pregnant women's tobacco use, SHS exposure, knowledge and attitudes towards tobacco use and exposure to advertising for and against tobacco products in Zambia and in the Democratic Republic of the Congo (DRC).

Material and methods

The Global Network tobacco survey

The National Institute of Child Health and Human Development's Global Network for Women's and Children's Health Research focuses on improving maternal and child health outcomes in the developing world; Global Network research units were chosen on the basis of scientific merit and included two in Africa: Zambia and the DRC. Briefly, the Global Network tobacco survey involved nine research units and included detailed questions about pregnant women's tobacco use (cigarettes and other forms of tobacco), exposure to SHS, attitudes towards tobacco use by women and exposure to advertising for and against tobacco products (15). The survey also included both closed- and open-ended questions to determine pregnant women's knowledge of the health hazards of smoking and SHS exposure. The face-to-face survey was administered by trained interviewers to a convenience sample of pregnant women identified at prenatal care clinics, hospitals or health centers, who were 18–46 years of age and beyond the first trimester of pregnancy.

The tobacco survey in Zambia and the DRC

In Zambia, the tobacco survey was conducted at the University Teaching Hospital and ten Urban District midwife-led maternity centers in Lusaka; in the DRC, the tobacco survey was conducted in three maternity hospitals in the central and peripheral areas of Kinshasa. Written consent was obtained for all willing, eligible women and ethics approval was obtained from the sponsoring universities and the data coordinating center, Research Triangle Institute. The surveys were administered between November 2004 and September 2005.

Tobacco use status

All pregnant women were asked: ‘Have you ever tried cigarette smoking, even one or two puffs?’ Those responding ‘yes’ were considered to have experimented with cigarettes. Among respondents who had experimented, those who had ever smoked daily and/or had smoked at least 100 cigarettes in their lifetime were considered to have ever been a regular cigarette smoker. Similarly, all pregnant women were asked if they had ever tried ‘any other forms of tobacco, besides cigarettes’? Those responding ‘yes’ were considered to have experimented with any other form of tobacco. Among respondents who had experimented, those who had ever used the product daily and/or had used the product at least 100 times were considered to have ever been a regular user of that product.

SHS exposure

All pregnant women were asked: ‘Is smoking of tobacco products allowed in your home?’ ‘How often are you indoors and around people who are smoking cigarettes or other types of tobacco products?’ and ‘How often are your children, 5 years or younger, indoors and around people who are smoking cigarettes or other types of tobacco products?’

Exposure to advertising for and against tobacco products

All pregnant women were asked if they had seen or heard advertising for tobacco products in the last 30 days. Those responding ‘yes’ were asked about the frequency and location of exposure. Similarly, all pregnant women were asked if they had seen or heard advertising against tobacco products in the last 30 days; those responding ‘yes’ were asked about the frequency and location of exposure.

Socioeconomic status

For Zambia, socioeconomic status (SES) was computed using the household asset index established by the World Bank (16). For the DRC, the household asset index for Cameroon was used, because an index for the DRC was unavailable (17).

Data analysis

Data analysis was performed using SAS version 9.1.3. We calculated descriptive statistics (frequencies, percentages, means and standard deviations) for each site, excluding missing data from the analysis. For each country, odds ratios and 95% confidence intervals were computed to assess the differences between literate and non-literate pregnant women for specific tobacco variables.

Results

A total of 1,915 women were screened and of these, 1,769 (92%) were eligible and 1,756 (99%) provided consent and completed the survey, 909 in Zambia and 847 in the DRC. The mean age of the pregnant women surveyed was 26.1 years (25.0 years in Zambia, 27.3 years in the DRC; Table 1). Most respondents lived in an urban setting (94.8% in Zambia, 61.8% in the DRC). A majority of respondents had completed 6–10 years of formal education (61.3% in Zambia, 52.7% in the DRC), and were literate (75.0% in Zambia, 90.8% in the DRC). In both countries, more than 85% of respondents were either married or were a member of a couple, and most were from the two highest SES quintiles.

Table 1. Participant demographics.
VariableZambia n = 909DRC n = 847Total n = 1,756
  1. DRC, Democratic Republic of the Congo; SD, standard deviation; SES, socioeconomic status.

Age, mean (SD)25.0 (5.5)27.3 (6.1)26.1 (5.9)
Municipality type9088441,752
 Urban, n (%)861 (94.8)522 (61.8)1,383 (78.9)
 Semi-urban, n (%)21 (2.3)322 (38.2)343 (19.6)
 Rural, n (%)26 (2.9)0 (0.0)26 (1.5)
Education9088461,754
 No education, n (%)41 (4.5)18 (2.1)59 (3.4)
 1–5 years, n (%)137 (15.1)92 (10.9)229 (13.1)
 6–10 years, n (%)557 (61.3)446 (52.7)1,003 (57.2)
 > 10 years, n (%)173 (19.1)290 (34.3)463 (26.4)
Literate, n (%)681 (75.0)769 (90.8)1,450 (82.6)
Marital status9098471,756
 Married/member of unmarried couple, n (%)829 (91.2)725 (85.6)1,554 (88.5)
 Other, n (%)80 (8.8)122 (14.4)202 (11.5)
SES index9038411,744
 Quintile 1, n (%)2 (0.2)0 (0.0)2 (0.1)
 Quintile 2, n (%)9 (1.0)0 (0.0)9 (0.5)
 Quintile 3, n (%)19 (2.1)22 (2.6)41 (2.4)
 Quintile 4, n (%)506 (56.0)273 (32.5)779 (44.7)
 Quintile 5, n (%)367 (40.6)546 (64.9)913 (52.4)

Tobacco use, SHS exposure and attitudes towards women's tobacco use

Respondents from the DRC were more than twice as likely as those from Zambia to report ever having tried cigarette smoking (14.1% in the DRC, 6.6% in Zambia; Table 2). In both countries, however, less than 1% of pregnant women had ever been a regular cigarette smoker, and very few thought it was acceptable for women in their community to smoke cigarettes.

Table 2. Pregnant women's tobacco use, secondhand smoke exposure, advertising exposure, knowledge and attitudes.
VariableZambia n = 909 n (%)DRC n = 847 n (%)Total n = 1,756 n (%)
  1. aResults exclude respondents without children 5 years or younger.

  2. bMay be greater than 100% because respondents were permitted to name more than one disease/condition.

  3. DRC, Democratic Republic of the Congo; SHS, secondhand smoke; SIDS, sudden infant death syndrome.

Cigarette use   
 Ever tried cigarette smoking60 (6.6)119 (14.1)179 (10.2)
 Ever a regular cigarette smoker3 (0.3)5 (0.6)8 (0.5)
 Think it is acceptable for women to smoke cigarettes17 (1.9)17 (2.0)34 (1.9)
Other tobacco product use   
 Ever tried other tobacco product20 (2.2)352 (41.8)372 (21.2)
 Ever a regular user of other tobacco product0 (0.0)3 (0.4)3 (0.2)
 Think it is acceptable for women to use other tobacco products13 (1.4)32 (3.8)45 (2.6)
SHS exposure   
 Live with one or more tobacco users213 (23.4)229 (27.0)442 (25.2)
 Smoking of tobacco products permitted in the home186 (20.5)144 (17.1)330 (18.9)
 Woman's exposure to tobacco smoke indoors (n)9088421,750
  Rarely or never596 (65.6)562 (66.7)1,158 (66.2)
  Sometimes188 (20.7)210 (24.9)398 (22.7)
  Frequently or always124 (13.6)70 (8.3)194 (11.1)
 Young children's exposure to tobacco smoke indoors (n)a4905411,031
  Rarely or never349 (71.2)402 (74.3)751 (72.8)
  Sometimes77 (15.7)104 (19.2)181 (17.6)
  Frequently or always64 (13.1)35 (6.4)99 (9.6)
Advertising exposure   
 Seen/heard advertising for tobacco products127 (14.0)100 (11.9)227 (13.0)
  Seen/heard one or more times a day4 (3.1)39 (39.0)43 (18.9)
  Seen/heard one or more times a week33 (26.0)34 (34.0)67 (29.5)
  Seen/heard one or more times a month90 (70.9)27 (27.0)117 (51.5)
 Seen/heard advertising against tobacco products192 (21.1)164 (19.5)356 (20.3)
  Seen/heard one or more times a day6 (3.1)41 (25.0)47 (13.2)
  Seen/heard one or more times a week39 (20.3)25 (15.2)64 (18.0)
  Seen/heard one or more times a month147 (76.6)98 (59.8)245 (68.8)
Think cigarette smoking harms woman's health879 (96.7)821 (97.5)1,700 (97.1)
 Specific disease/condition that can be namedb   
  Asthma112 (12.3)9 (1.1)121 (6.9)
  Bronchitis55 (6.1)11 (1.3)66 (3.8)
  Lung disease407 (44.8)198 (23.5)605 (34.6)
  Cough496 (54.6)182 (21.6)678 (38.7)
  Lung cancer162 (17.8)107 (12.7)269 (15.4)
  Cancer, other80 (8.8)15 (1.8)95 (5.4)
  Heart disease108 (11.9)38 (4.5)146 (8.3)
  Don't know42 (4.6)40 (4.8)82 (4.7)
Think cigarette smoking during pregnancy harms baby751 (82.7)768 (91.2)1,519 (86.8)
 Specific disease/condition that can be namedb   
  Lower birth weight98 (10.8)44 (5.2)142 (8.1)
  Preterm delivery62 (6.8)5 (0.6)67 (3.8)
  Infant death58 (6.4)32 (3.8)90 (5.1)
  Respiratory/breathing problem303 (33.3)219 (26.0)522 (29.8)
  Crib death/SIDS37 (4.1)3 (0.4)40 (2.3)
  Don't know321 (35.3)321 (38.1)642 (36.7)
Think SHS is harmful754 (82.9)704 (83.6)1,458 (83.3)
 Specific disease/condition that can be namedb   
  Lung cancer95 (10.5)32 (3.8)127 (7.3)
  Heart disease79 (8.7)27 (3.2)106 (6.1)
  Disease in children19 (2.1)4 (0.5)23 (1.3)
  Respiratory/breathing problem509 (56.3)284 (33.8)793 (45.5)
  Don't know168 (18.6)269 (32.0)437 (25.1)

Few respondents from Zambia had ever tried any other (non-cigarette) tobacco product (2.2%). In contrast, in the DRC, more than four in ten respondents (41.8%) reported ever having tried any other tobacco product, usually snuff, and nearly half (49.7%) of those who had never tried thought they would do so in the next year (data not shown). Few respondents in either country thought it was acceptable for women in their community to use other (non-cigarette) tobacco products.

In both countries, respondents were most likely to report that they and their young children (< 5 years old) were rarely or never exposed to tobacco smoke indoors. However, about one in five pregnant women reported that tobacco smoking was permitted in their home (20.5% in Zambia, 17.1% in the DRC), and a minority reported that they were frequently or always exposed to tobacco smoke indoors (13.6% in Zambia, 8.3% in the DRC) and that their children were frequently or always exposed to tobacco smoke indoors (13.1% in Zambia, 6.4% in the DRC). About one in four respondents lived in a household where one or more other people used tobacco products.

Exposure to advertising for and against tobacco products

In Zambia, 14.0% of pregnant women reported having seen or heard advertising for tobacco products, while 21.1% reported having seen or heard advertising against tobacco products in the last 30 days. The frequency of exposure to both types of advertising was typically very low (one or more times a month). The most commonly cited channels of exposure to both pro- and anti-tobacco advertising were television, radio, magazines and community or other events (data not shown).

In the DRC, 11.9% of pregnant women reported having seen or heard advertising for tobacco products, while 19.5% reported having seen or heard advertising against tobacco products in the last 30 days. However, daily or weekly exposure was reported by 73% of those exposed to pro-tobacco advertising, compared with only 40.2% of those exposed to anti-tobacco advertising. Commonly cited channels for pro-tobacco advertising were television and billboards; commonly cited channels for anti-tobacco advertising were television, church and transport (data not shown).

Knowledge of the health hazards of cigarette smoking and SHS exposure

In both countries, nearly all pregnant women responded affirmatively when asked if ‘a woman who smokes cigarettes harms her own health, or not’. However, when asked to name health effects or diseases caused by cigarette smoking, it was apparent that respondents' knowledge was limited. In Zambia, cough was the most frequent response (54.6%), followed by lung disease (44.8%), lung cancer (17.8%), asthma (12.3%) and heart disease (11.9%). In the DRC, respondents most frequently mentioned lung disease (23.5%), followed by cough (21.6%) and lung cancer (12.7%).

In both countries, most pregnant women (> 82%) responded affirmatively when asked if a mother who smokes cigarettes during pregnancy can harm her unborn baby's health. However, more than one-third of pregnant women in both countries responded ‘don't know’ when asked to name a specific health effect or disease caused by smoking during pregnancy. The next most common response in both countries was respiratory/breathing problem (33.3% in Zambia, 26.0% in the DRC). Lower birth weight was mentioned by 10.8% of pregnant women in Zambia and 5.2% of pregnant women in the DRC.

In both countries, more than 80% of pregnant women responded affirmatively when asked ‘do you think the smoke from other people's cigarettes is harmful, or not?’ When asked to name a specific health effect or disease caused by exposure to other people's cigarette smoking, the most common response in both countries was respiratory/breathing problem (56.3% in Zambia, 33.8% in the DRC). In Zambia, 10.5% of respondents mentioned lung cancer, and 8.7% mentioned heart disease. In the DRC, other responses were very uncommon.

Relation between literacy and tobacco exposure

In both Zambia and the DRC, literate pregnant women were significantly less likely to live with other tobacco users, to live in a home where tobacco smoking was permitted and to report they or their young children were frequently or always exposed to tobacco smoke indoors, compared to other women (Table 3). However, literacy was not significantly associated with whether or not pregnant women had ever tried a tobacco product, with the perceived acceptability of women's tobacco use or with their exposure to pro-tobacco advertising. In the DRC, literate pregnant women were more likely than illiterate women to report exposure to anti-tobacco advertising.

Table 3. Relationship of literacy to tobacco variables for pregnant women in Zambia and DRC.
 ZambiaDRC
 LiterateOdds Ratio (95% CI)p-ValueLiterateOdds Ratio (95% CI)p-Value
 Yes N = 681 %No N = 227 %Yes N = 769 %No N = 78 %
  1. DRC, Democratic Republic of the Congo; SHS, secondhand smoke; CI, confidence interval.

Tobacco use and SHS exposure
 Ever tried cigarette or other forms of tobacco6.57.00.91 (0.50, 1.65)0.761714.510.41.46 (0.68, 3.12)0.3245
 Live with one or more tobacco users19.834.40.47 (0.34, 0.66)< 0.000125.739.70.53 (0.32, 0.85)0.0080
 Tobacco smoking permitted in the home17.529.50.51 (0.36, 0.72)0.000116.226.00.55 (0.32, 0.95)0.0301
 Women frequently or always exposed to tobacco smoke indoors11.819.40.55 (0.37, 0.83)0.00387.120.80.29 (0.16, 0.54)< 0.0001
 Young children frequently or always exposed to tobacco smoke indoors10.919.10.52 (0.30, 0.90)0.01745.612.70.41 (0.18, 0.95)0.0325
Attitudes
 Think it is acceptable for women to smoke cigarettes1.53.10.47 (0.18, 1.25)0.12002.11.31.62 (0.21, 12.41)0.6373
 Think it is acceptable for women to use other tobacco products1.02.60.38 (0.13, 1.15)0.07603.83.90.97 (0.29, 3.27)0.9633
Advertising exposure
 Seen/heard pro-tobacco advertising14.412.81.15 (0.74, 1.79)0.543412.55.22.62 (0.94, 7.33)0.0573
 Seen/heard anti-tobacco advertising21.819.41.16 (0.79, 1.69)0.446920.59.12.58 (1.16, 5.73)0.0158

Discussion

To our knowledge, this is the first study to examine pregnant women's knowledge, attitudes and behavior regarding tobacco use and SHS exposure in the DRC or Zambia. In both countries, a small percentage of pregnant women had ever tried cigarettes (< 15%) and very few had ever been a regular smoker (< 1%). However, about four in ten DRC respondents had tried snuff, and many others said they intended to do so in the future. About 10% of pregnant women and young children were frequently or always exposed to SHS and this level of exposure was significantly more common among illiterate pregnant women and their young children. In both countries, pregnant women's knowledge of the health hazards of cigarette smoking was extremely limited, and more than 10% of respondents had been exposed to tobacco advertising in the last 30 days.

Our results are consistent with the available data suggesting that female cigarette smoking is currently quite low in most countries of sub-Saharan Africa (18, 19). However, the Global Youth Tobacco Survey (GYTS), a school based survey of students aged 13–15, has determined that in many regions of the world, including Africa, the difference between boys' and girls' cigarette smoking is far narrower than that between adult men and women (20). The 2002 Zambia GYTS found only modest differences between boys' and girls' cigarette smoking (boys: 10.8–14.9%; girls: 8.2–12.4%) and use of other tobacco products (boys: 16.4–20.0%; girls: 16.3–22.9%) (21). This suggests that Zambia, like some other African countries, may be poised for far higher tobacco use rates among women. The GYTS has not been conducted in the DRC.

The use of pipes, snuff and rolled tobacco leaves is believed to be widespread in sub-Saharan Africa (22). The use of smokeless tobacco, which encompasses a very diverse group of products, has been studied in South Africa, Tanzania and Sudan (23–26). In addition to the potential hazards of use during pregnancy, smokeless tobacco products contain nicotine, numerous carcinogens and other toxicants, and cause cancers of the oral cavity, esophagus and pancreas (27). Preliminary evidence suggests that in the DRC, many pregnant women view snuff and chewing tobacco as forms of medicine and use these products to treat flu, colds and other common ailments, for their pharmacological effects or instead of alcohol. A better understanding of pregnant women's misperceptions about these forms of tobacco is urgently needed.

Exposure to SHS poses a serious health hazard for adults and children (28, 29). Maternal exposure to SHS during pregnancy is causally related to a small reduction in infant birth weight, and postnatal exposure to SHS is causally related to sudden infant death syndrome. Additionally, suggestive evidence indicates a relation between maternal exposure to SHS during pregnancy and preterm delivery. In children, SHS exposure increases the risk for acute lower respiratory infections, middle ear diseases and asthma. In adults, SHS exposure causes coronary heart disease and lung cancer. Particularly in countries where few women smoke, such as Zambia and the DRC, research is needed to define culturally acceptable ways for women to create smoke-free home environments for themselves and their children. Effective strategies to prevent and control tobacco use by men, including policy measures and family- and community-based approaches, will significantly benefit the health of women and children as well.

Although overall knowledge was low, pregnant women in Zambia were somewhat more knowledgeable about the hazards of active smoking and SHS exposure than their counterparts in the DRC, despite higher literacy rates in the DRC. This may be attributed to the more urban setting of the Zambia study, differences in the availability of health information or other factors. In both countries, pregnant women's limited knowledge of the health hazards of smoking and SHS exposure is a serious challenge to tobacco control and prevention efforts. Health warning messages on tobacco packages, now mandatory in many countries, are a cost-effective way of increasing public knowledge (30). Large, picture-based warnings have greater effectiveness than small, text-only messages, and may be especially useful in reaching young people, those with little education and low levels of literacy and in countries where multiple languages are spoken (31–33). This strategy should have particular appeal in low- and middle-income countries because, unlike most educational interventions, the financial cost of health warning messages is borne entirely by tobacco manufacturers. While most African countries require tobacco health warning messages, currently only one country (Mauritius) requires picture-based warnings.

Tobacco advertising is an important factor promoting tobacco use (34–37). In both countries, some pregnant women reported exposure to tobacco advertising (Zambia: 14%; DRC: 11.9%). The Framework Convention on Tobacco Control (FCTC), the first treaty ever negotiated under the auspices of the World Health Organization, requires parties to the treaty to put in place a comprehensive ban on all tobacco advertising, promotion and sponsorship, consistent with national law (38). Zambia, but not the DRC, is a party to the FCTC. At present, Zambia does not ban any form of tobacco advertising, while the DRC employs a partial ban; however, partial advertising bans have not been found to be effective, because they allow advertising to be shifted from venues where they are banned to those where they are not (39).

In many African countries, including Zambia and the DRC, maternal and child health outcomes are often poor (40). The World Health Organization's African region has the highest neonatal mortality rate in the world (43/1,000 live births) and accounts for 43% of global deaths in children under age five. Additionally, 19 of the 20 countries with the highest maternal mortality ratios are in the African region. African women bear the burden of nearly half of all global maternal deaths as a result of pregnancy and childbirth; overall maternal mortality is 910/100,000 live births. The WHO African Regional Health Report notes that efforts to improve maternal and child health outcomes are hampered by poverty, illiteracy, weak health systems, a shortage of skilled health workers, armed conflict and humanitarian emergencies, the HIV/AIDS epidemic and other factors.

The current relatively low rates of tobacco use by women and men are one of the few positive health indicators in the African region. However, there is already evidence that this is changing. Many developing countries are undergoing a ‘risk transition’, wherein traditional risk factors for poor health associated with poverty have been joined by risk factors of affluence, because of marked changes in global patterns of consumption, particularly of food, alcohol and tobacco (41). Africa has not been exempt from this risk transition; increasingly, addressing non-communicable disease risk factors, such as tobacco use, is recognized as central to improving the health, social and economic development of African countries (42, 43).

Our study has several limitations. In both countries, we surveyed a convenience sample of pregnant women seeking care at maternity clinics. Each country's sample is not nationally representative, and is also not population-based; as demonstrated by the paucity of respondents in the lower SES quintiles, the most disadvantaged women were under-represented. Because the survey relied on self-report in cultures with strong social pressure against women's tobacco use, the findings may underestimate the scope of the problem. Finally, studies of pregnant women's tobacco use and SHS exposure should be conducted in other countries in sub-Saharan Africa to provide a better understanding of the regional problem.

Averting a rise in tobacco use by women in developing countries has long been regarded as a key public health priority (44). In settings where pregnancy outcomes are already often poor, such as in Zambia, the DRC and many other African countries, a rise in pregnant women's tobacco use and SHS exposure has the potential to dramatically worsen health outcomes. Our findings suggest that there remains a critical ‘window of opportunity’ to prevent an increase in tobacco use and SHS exposure among pregnant women in both Zambia and the DRC. However, pregnant women's limited knowledge of the health hazards of smoking, and the exposure of some to tobacco advertising, are troubling signs. We suggest that implementing evidence-based strategies to prevent and control tobacco use will be crucial to promoting and protecting maternal and child health in these two African countries.

Acknowledgements

Funding for the study was provided by the U.S. National Institute of Child Health and Human Development (UO1 HD043475, UO1 HD043464 and UO1 HD040607), the U.S. National Cancer Institute, the U.S. Department of Health and Human Services' Office on Women's Health and the Bill and Melinda Gates Foundation. The manuscript was approved for publication by the National Cancer Institute and the National Institute of Child Health and Human Development. The authors appreciate the efforts of the field staff who administered the survey and the pregnant women who participated.

Disclosure of interest: Dr. Bloch provided depositions on behalf of the US government in the US Department of Justice lawsuit, USA v. Philip Morris USA, Inc. et al., as part of her official duties. All other authors report no competing interests.

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