International Journal of Hygiene and Environmental Health
Maternal occupation and the risk of major birth defects: A follow-up analysis from the National Birth Defects Prevention Study
Introduction
Associations between maternal occupations and certain birth defect outcomes have been studied, though not thoroughly. Studies have shown oral clefts (Cordier et al., 1992, Lorente et al., 2000), neural tube defects (NTDs) (Brender et al., 2002), spina bifida (Blatter et al., 1996), and chromosomal single birth defects (Chia et al., 2003) to be associated with the maternal occupations of janitors or cleaners. A French study found that nurses, laboratory workers, hairdressers, and cleaners may be exposed to solvents and that maternal exposure to solvents was associated with major malformations, including oral clefts, urinary malformations, and male genital malformations (Garlantezec et al., 2009). Similarly, a study of births from 1968 to 1980 reported that women who worked as nurses had a higher risk of offspring with anencephaly/spina bifida, coarctation of aorta, genital and urinary system defects (Matte et al., 1993). Mexican-American healthcare workers have also been shown to have an elevated risk of neural tube defects (Brender et al., 2002). A Danish study found an increased risk for ‘major’ malformations among laboratory workers who worked with radioimmunoassays, radiolabelling, and organic solvents (Zhu et al., 2006).
Few studies have had an adequate sample size to use precisely defined birth defects and more specific occupational categories. Furthermore, the occupational characteristics such as number of jobs, work hours, and the demographic/life styles related to these occupations with potentially high risk have not been studied. In addition, many studies did not report adjusted effect measure estimates. Older studies were not able to take into consideration more recent changes in the job place such as use of personal protective equipment, chemical exposures, and the integration of women into jobs once held by men (Matte et al., 1993, Zhang et al., 1992, Savitz et al., 1996, Hemminki et al., 1981). Although folic acid supplementation prior to and during pregnancy has been shown to be protective against NTDs, cleft lip with/without cleft palate, and possibly other birth defects, its potential interactive effect with occupation has not been explored (MRC, 1991, van Rooij et al., 2004, Wilcox et al., 2007).
The purpose of this analysis is to address these limitations and expand our recent case–control analysis. Previously, we used National Birth Defects Prevention Study (NBDPS) data including over 12,000 working women and looked at 24 maternal occupations and 45 birth defect outcomes within 9 organ systems for births between 1997 and 2003 (Herdt-Losavio et al., 2010). Results for five maternal occupational groups from that study were of considerable interest because they were large groups and each was associated with several birth defects. Using the same national dataset with one more year of interview data, the objective of this subsequent in-depth analysis is to further evaluate the association between these five maternal occupational groups, including subgroups of healthcare workers, cleaners, scientists, personal service workers, and teachers, and specific birth defects. In addition, these associations were examined for effect measure modification by folic acid. A dose response relationship for work hours and number of jobs held was explored, and socio-demographic/life style characteristics related to these jobs were described.
Section snippets
Design and study population
The current analysis used data from the NBDPS, which is an ongoing, multi-center, case–control study (Yoon et al., 2001). Birth defects with known etiologies, such as single-gene conditions or chromosomal abnormalities, were excluded from the NBDPS. A total of ten centers (California, Iowa, Massachusetts, New Jersey, New York, Texas, CDC/Atlanta, North Carolina, Arkansas, and Utah) contributed data for infants with estimated delivery dates between October 1, 1997 and December 31, 2004. Each
Results
The response proportions of the telephone interview were 69% for the cases and 65% for the controls, respectively. At the time of interview, about 72% of the mothers (both the cases and the controls) reported being employed. There were significant differences between all case mothers combined and control mothers in terms of age, body mass index, education, parity, pre-pregnancy diabetes, smoking and study site (Herdt-Losavio et al., 2010). These factors were controlled in the multivariable
Discussion
This study found that maternal occupation as a nurse was positively associated with an increase in hydrocephalus and LVOTO. However, women having other health care occupations such as physicians and dentists were not positively associated with any birth defects. Although the evidence was not consistent in all previous studies, our findings for nurses were consistent with previous studies of maternal occupation as a nurse and hydrocephalus or other central nervous system defects (Brender et al.,
Acknowledgements
This study was supported by a cooperative agreement from the Centers for Disease Control and Prevention, Grant No. U50/CCU223184. We would like to thank the participating families, staff and scientists from all National Birth Defects Prevention Study sites (Arkansas, California, Georgia, Iowa, Massachusetts, New Jersey, North Carolina, New York, Texas and Utah). The findings and conclusions of this report are those of the authors and do not necessarily represent the views of the Centers for
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