Employment and low birth weight in black women

Abstract

Recent studies have not shown adverse effects of employment during pregnancy on the pregnancy outcome, but most have not successfully distinguished factors due to work-related physical and mental strain from differences in social, economic and cultural characteristics between employed and non-employed women. We analyzed data from the Alameda County Case-Control Study of Low Birth Weight to address the question of employment as a risk factor for low birth weight in more depth. Subjects in the study were singleton infants without congenital malformations born in 1987 to black or white, non-hispanic residents of Alameda County, a large urban community in California. Cases were all infants weighing less than 2500 g at birth; controls were chosen at random from the infants weighing 3000 g or more. The mothers of 377 black cases, 389 black controls, 233 white cases and 239 white controls could be located and interviewed. This analysis excluded the white women because evidence of response bias in regard to employment was found for them but not for black women. The percentage of black women in the study who were employed during pregnancy was 49.9%. Employment was associated with a significantly lower relative risk of low birth weight before and after controlling for age, parity, smoking, heavy alcohol use, prior low birth weight infants and low pre-pregnancy weight. After adjustment for known risk factors foe low birth weight, employment explained more of the variance of low birth weight than other commonly used measures of ‘social class’, including income, education and marital status. Employment had a beneficial association with low birth weight for each of three levels of socioeconomic status as measured by a combined education and income scale. The results suggest that the association of employment with a better birth weight outcome acts outside of measured changes in risk behavior of pregnant women at the work place and is independent of socioeconomic status. The study did not determine whether this association is due to self-selection of low risk women into the work force or whether employment itself has a beneficial effect on the pregnant women and her infant. Studies of work related-fatigue and occupational hazards must take the beneficial, independent association of employment with low birth weight into account. Determining whether interventions that increase employment in pregnant women cause better pregnancy outcome has important implications for social welfare and public health policy.