Investigating sociodemographic factors associated with Iodine deficiency among pregnant women in developing and developed countries: systematic review

Abstract

Background Iodine deficiency (ID) is one of the major public health issues globally. It is considered as the primary cause of the potentially preventable brain damage among children as well as stillbirth and spontaneous abortion during pregnancy. The latest global estimate is that approximately 2 billion individuals have inadequate dietary iodine intake, including 241 million school-aged children. Considerably, pregnant women, infants, and children are the most vulnerable groups with ID because of the potentially irreversible detrimental outcomes. Although ID may be more serious in developing countries, it also equally affects developed countries. Identifying the risk factors/predictors of any public health issue is a priority of health care investigators to prevent diseases to occur. The impact of dietary iodine intake and practices such as iodised salt and iodine supplementation on ID were already systematically investigated and there were controversial results about their effect on ID outcomes among pregnant women. However, no systematic reviews have previously been conducted for sociodemographic factors as it is more likely to be associated with dietary iodine intake and other practices. Therefore, the aim of this study was to systematically investigate the association between sociodemographic factors and ID among pregnant women over the world. Methods This systematic review used three databases to search for relevant articles and examine the association between sociodemographic factors and ID among pregnant women globally: Medline Ovid, Embase, and Web of Science. It followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines for reporting the resultant articles from each step of screening and selecting studies. Articles were screened by title, abstract, and full text based on the eligibility criteria of included studies. This review only included observational studies investigating the exposure of interest. The PICO (i.e. Population, Indicators, Comparison, Outcome) criteria was used to effectively include the relevant articles and reduce the chance of selection bias. The population of interest comprised pregnant women at any gestational age and within any age group. Indicators included sociodemographic factors, since all included studies compared (comparison) pregnant women within different sociodemographic categories such as maternal age, ethnicity, education/and knowledge, socioeconomic status, parity/and family size, and geographical variation. The outcome of interest in this review was ID measured by Urinary iodine concentration (UIC), urinary iodine to creatinine ratio (UI/Cr ratio), and urinary iodine excretion (UIE). Findings from included articles were extracted and analyzed and a risk of bias assessment was performed for all included studies using the National Heart, Lung, and Blood Institute (NHLBI) tool. Finally, a narrative synthesis, rather than a meta-analysis was undertaken due to the heterogeneity of the included studies and their respective findings. Results There were 22 cross-sectional studies and three cohort studies included in this review. Not all studies examined all of the sociodemographic factors, but most of them assessed more than one or two exposure factors. This review found considerably strong evidence to suggest that women with high education levels, socioeconomic status, and parity levels had lower risk of ID whilst those with large family size at higher risk. Furthermore, it was also found that race or ethnicity was substantially associated with iodine status in pregnant women. However, there was no consistent evidence to determine the direction of the association of maternal age and geographical variation factors with ID because of conflicting evidence across different studies.

Conclusions

This study reported the most common socio