PretermBirth and PrenatalMaternal Occupation: The Role of Hispanic Ethnicity and Nativity in a Population-Based Sample in Los Angeles, California

The prevalence of preterm birth (PTB) in the United States increased over the past decades with persistent racial/ethnic disparities, and it remains the main cause of infant mortality. Hispanic women have on average a higher prevalence of PTB than non-Hispanic White women, and risks tend to vary by nativity (US-born vs foreign-born). These disparities remain poorly understood and have not to date been explained by social or demographic factors. The US Hispanic population is highly diverse with regard to cultural, behavioral, and socioeconomic factors. Research considering underlying differences in occupational or environmental influences to explain ethnic disparities in risk for PTB is sparse and has largely not considered nativity. Differences related to ethnicity and nativity have been reported for behavioral reproductive risk factors including maternal smoking, alcohol consumption, or diet, but research has not addressed whether PTB risks related to maternal occupation differ by ethnicity and nativity. Occupational exposure may increase risks for PTB by interrupting the prenatal neuroendocrine balance, thereby promoting premature parturition, and these adverse occupational influences may possibly affect Hispanic populations in the United States disproportionally and may possibly also be modified by nativity. Several studies involving mainly European populations and a handful of US studies including mainly non-Hispanic populations have attempted to elucidate associations between PTB and maternal work, but findings have been inconclusive. These earlier studies have generally not considered potential influences of ethnicity, race, or nativity on associations between maternal work and PTB. In fact, non-US studies have not considered ethnicity, race, or nativity at all. US studies have generally adjusted for race/ ethnicity but have not accounted for nativity. A few of the earlier studies were registry based, involving a range of occupations, but lacked information regarding whether women worked in the registered job during pregnancy. Registry-based findings from Sweden did not consider racial/ ethnic population composition or nativity but suggested that working as building cleaner, mechanic, or food manufacturer was associated with slightly higher odds ratios for PTB. One earlier survey in North Carolina that reported increased odds ratios for PTB among electrical equipment workers and janitors adjusted for ethnicity and race but did not consider nativity. Several previous studies from different countries focused on selected types of exposures, such as physical or psychological demand or shift work. Findings were inconclusive, and possible modifying influences of ethnicity or nativity were not examined. Reports from Canada and Europe suggested moderately increased risks for PTB related to physical and psychological job strain. By contrast, a Dutch study involving a population that was part northern European, part northern African, part Surinamese, and part other, unspecified origins showed that neither physical demand nor exposure to toxic substances influenced PTB; however, results by race/ethnicity or nativity were not reported. The Danish National Birth Cohort, a mainly northern European population, found no association between PTB and occupationrelated infectious exposures. Finally, effects for single occupational groups, especially nurses, have been reported, 26,31 with increased risks seen in North Carolina but not in Finland. Findings from the US Nurses’ Health Study suggested increased PTB risks in relation to some work exposures. Potential differences in effects by race/ethnicity and nativity among nurses or health care workers were not examined in any of these studies. A sole study to date has been Objectives. We investigated preterm birth (PTB) in relation to maternal occupational exposure and whether effect measures were modified by Hispanic ethnicity and nativity in a population-based sample with high proportion of Hispanics. Methods. We used a case-control study (n = 2543) nested within a cohort of 58 316 births in Los Angeles County, California, in 2003. We categorized prenatal occupations using the US Census Occupation Codes and Classification System and developed a job exposure matrix. Odds ratios for PTB were estimated using logistic regression. Results. Odds ratios for PTB were increased for all women in health care practitioner and technical occupations, but the 95% confidence intervals included the null value; effects were more pronounced among Hispanics. We estimated elevated odds ratios for foreign-born Hispanic women in building and grounds cleaning and maintenance occupations. Shift work and physically demanding work affected births among US-born but not foreign-born Hispanics. Conclusions.Hispanicwomen are at particular risk for PTB related to adverse prenatal occupational exposure. Nativity may moderate these effects on PTB. Maternal occupational exposures likely contribute to ethnic disparities in PTB. (Am J Public Health. 2014; 104:S65–S72. doi:10.2105/AJPH.2013.301457) RESEARCH AND PRACTICE