Secondhand smoke exposure inside the house and low birth weight in Indonesia: Evidence from a demographic and health survey

INTRODUCTION Secondhand smoke (SHS) exposure during pregnancy among non-smoking women is associated with mortality and morbidity risks in infants. However, little is known about SHS inside the house and low birth weight in newborns. This study aims to assess the prevalence, level, and frequency of SHS exposure inside the house and investigate their associations with low birth weight. METHODS We used the Indonesian Demographic and Health Survey (IDHS) 2017, a large-scale, nationally representative survey. Women aged 15–49 years who had given birth in the last five years before the study and their husbands were interviewed (n=19935). Two dependent variables included low birth weight (LBW) and birth weight. RESULTS In all, 78.4% of mothers were exposed to SHS inside the home, of whom 7.2% had LBW children. Compared to non-exposed to SHS mothers, those exposed to SHS were younger, had their first birth before the age of 20 years, were married, lower educated, non-workers, lived in rural areas, were grand multipara, had pollution from cooking fuel, cooked in a separate building, and had a higher risk of delivering a lower birth weight (AOR=1.16; 95% CI: 1.02– 1.33). CONCLUSIONS Exposure to SHS inside the home was significantly associated with LBW. Given the high prevalence of smoking, relevant policies and health promotion are needed. Research Paper | Population Medicine Popul. Med. 2023;5(June):17 https://doi.org/10.18332/popmed/168620 2 basis6. Based on Demographic and Health Survey data collected between 2008 and 2013, from 30 lowand middle-income countries (LMICs), daily SHS exposure accounted for a more significant population-attributable fraction of stillbirths than active smoking, which was 14% in Indonesia. This number is the highest among the other 30 LMICs7. Indonesia has compiled various regulations governing public protection from the dangers of exposure to cigarette smoke. One of them is the adoption of no-smoking zones in various public places and workplaces, especially in schools and hospitals. However, the World Health Organization (WHO) notes that regulations regarding smoke-free areas in public areas in Indonesia are still relatively low compared to other South-East Asian countries, and in accordance with the geographical distribution as well as socioeconomic disparity, in urban settings, the wealthier and more educated population were more likely to adopt a smoke-free policy8. Given the implications for child mortality, a significant reduction in the prevalence of LBW is necessary to achieve the Sustainable Development Goals, and there is a similar need to strengthen the implementation of the Framework Convention on Tobacco Control (FCTC) of the WHO in all countries9. Only a few robust studies examined a clear association between exposure to SHS inside the house and birth outcomes, especially in Indonesia10,11. This study contributes to filling the knowledge gap in SHS exposure inside the house and low birth weight in Indonesia by using the evidence of large-scale population-based data and taking into account SHS frequency and LBW, neither of which have been presented in previous studies. This study assesses the prevalence, level, and frequency of SHS exposure inside the house and their associations with birth outcomes. METHODS Data sources We used data from the latest 2017 Indonesia Demographic and Health Survey (IDHS) survey, a nationally representative, large-scale, and repeated cross-sectional household survey collecting population, health, and nutrition data. All evermarried women aged 15–49 years who had given birth in the last five years before the survey in sampled households are eligible for an interview using a standard self-reported questionnaire12. Women were chosen to give birth during the last five years before the survey to prevent bias in memory recall from mothers. The total sample size in the study was 19935. Respondents in the 2017 IDHS read a written informed consent statement before each interview. The statement also included voluntary participation, refusal to answer questions or termination of participation at any time, and confidentiality of identity and information. Measurement Two main independent variables were the exposure to SHS inside the house and the frequency of SHS exposure. The information about SHS inside the house is obtained from two types of 2017 IDHS questionnaires: the household questionnaire and the women’s questionnaire. The information regarding SHS exposure at home was derived from the question at the household questionnaire: ‘How often does anyone smoke inside your house? (daily, weekly, monthly, less than monthly, never)?’. To ascertain whether the mother in the household smoked or not, we linked smoking data from the household questionnaire to the women’s questionnaire through their unique identifier codes. In the women’s questionnaire, there are two questions related to smoking habits: 1) ‘Do you currently smoke?’ (every day, sometimes, not at all); 2) ‘In the past, have you ever smoked?’. (every day, sometimes, not at all.) All household members and mothers who answered ‘never’ or ‘not at all’ were included in the ‘non-exposed’ SHS group. Meanwhile, the SHS ‘exposed’ group consists of: 1) household members who do not smoke, but the mother smokes; 2) household members who smoke, but the mother does not smoke; and 3) all household members and mothers who answered ‘daily, weekly, monthly, less than monthly, every day, sometimes’. Then, a binary variable (not exposed vs exposed) was created to measure exposure to SHS inside the house, where one or more adults smoke commercial cigarettes, cigars (including kretek cigarettes or unfiltered cigarettes of Indonesian origin), and other country-specific smoking products (including pipes, cigars, shisha, chewing tobacco, and chewing betel nut with tobacco). The information regarding SHS exposure frequency at home was derived from the question on the household questionnaire in the 2017 IDHS: ‘How often does anyone smoke inside your house?’ (daily, weekly, monthly, less than monthly, never). SHS frequency was then classified as: not exposed, less than once a month, monthly, weekly, and daily. Two outcome variables related to the self-reported birth outcomes are LBW and birth weight. We treated LBW (<2500 g; compared to ≥2500 g) as a categorical variable. Birth weight (g) was treated as a continuous variable. Potential covariates Demographic and socioeconomic characteristics included maternal age, age at first birth, marital status, maternal education level, family size, mother’s occupation, husband’s education level, residence (urban or rural), parity, birth interval, birth order, wealth index, cooking fuel, and kitchen location. The wealth index is a composite measure of a household’s cumulative living standard or ownership of selected assets. The resulting combined wealth index has a mean of zero and a standard deviation of one. Once it is obtained, national-level wealth quintiles are obtained by assigning the household score to each de jure household member, ranking each person in the population by their score, and then dividing the ranking into five equal parts, from quintile one (lowest=poorest) to quintile five (highest=wealthiest), each having approximately 20% Research Paper | Population Medicine Popul. Med. 2023;5(June):17 https://doi.org/10.18332/popmed/168620 3 of the population. Cooking fuel consists of electricity or gas, kerosene, coal or lignite, charcoal, and wood or straw (including grass, shrubs, and plant residues). Clean cooking fuels include electricity or gas, while pollutant cooking fuels include kerosene, coal or lignite, charcoal, and wood or straw (including grass, shrubs, and plant residues). Statistical analysis The data were analyzed using SPSS version 25. The proportions and chi-squared tested the differences between SHS exposure and demographic and socioeconomic characteristics inside the house. Logistic regression analyses measured the relative odds of associations between SHS exposure and frequency inside the house and LBW. The general linear model assessed the relationships between SHS exposure and frequency inside the house and birth weight. All multivariable models were used to control for covariates. Backward elimination as the variable selection procedure retained critical confounding variables, resulting in a slightly richer model. The overall model was also evaluated using the goodness-of-fit test and the likelihood ratio test. RESULTS The characteristics of the participants are presented in Table 1. In all, 78.4% of the mothers were exposed to SHS in the household, with 7.2% of those with LBW being exposed to SHS. Compared with non-SHS exposure mothers, mothers exposed to SHS were aged 15–24 years, had their first birth before 20 years of age, were married, had a lower education, were non-workers, lived in a rural area, had grand multiparas, had pollution from cooking fuel, and cooked in a separate building. All the indicators were statistically significant at p<0.05, except for the husband’s occupation and birth interval, which were not different in exposure to SHS. Table 2 shows that the mean birth weight was significantly associated with SHS exposure inside the house. After adjusting for the covariates, mothers exposed to SHS had children with a mean birth weight of 71.6 g (p<0.01) lower than that of mothers who were not exposed to SHS. Compared to non-SHS exposure, mothers who were exposed to SHS showed a 1.16-fold increase in the odds of having LBW children (AOR=1.16; 95% CI: 1.02–1.33, p<0.05). For SHS exposure frequency, mothers exposed to SHS daily had children with a mean birth weight of 63.4 g (p<0.01) lower than that of mothers who were not exposed to SHS. Compared to non-SHS exposure, mothers who were exposed to SHS weekly and daily showed an increase in the odds of having LBW children (AOR=1.33; 95% CI: 1.03–1.71, p<0.05 and AOR=1.18; 95% CI: 1.01–1.38, p<0