Objective: The purpose of this study was to evaluate the association between the prevalence of birth defects among maternal and paternal occupation groups in Singapore for live births between January 1, 1994, and December 31, 1998, and to determine whether there are certain demographic risk factors and maternal and/or paternal occupation groups that are associated with an increased risk for birth defects versus chromosomal single birth defect, nonchromosomal single birth defect, and multiple birth defects.
Study design: This was a retrospective study. Information on live births (Singapore National Registry of Births and Deaths) and birth defect cases (National Birth Defects Register) were studied. Other information included the mother's date of birth, ethnic group, highest educational qualification, and the occupation of the mother and the father. Cox regression analysis was used to determine whether certain demographic and occupational factors were associated with the three groups of birth defects.
Results: Of a total of 237,755 live births, there were 3276 birth defect cases (nonchromosomal single birth defect, 1869 cases; chromosomal single birth defect, 197 cases; and multiple birth defects, 1210 cases). Increased risks for all types of birth defects were observed with advancing gestational age. Occurrence of nonchromosomal single birth defect and multiple birth defects were significantly higher for multiple births compared to singleton births. Significant associations were found with the use of "legislators, senior officers, and managers" as reference: Maternal occupation of "cleaners, laborers, and related workers" with chromosomal single birth defect anomalies (adjusted risk ratio, 4.86; 95% CI, 1.07-22.14); paternal occupation of "plant and machine operators and assemblers" (adjusted risk ratio, 1.50; 95% CI, 1.14-1.98) with nonchromosomal single birth defect; "production craftsmen and related workers" and "cleaners and laborers and related workers" with nonchromosomal single birth defect (adjusted risk ratio, 1.42; 95% CI, 1.10-1.82; and adjusted risk ratio, 1.43; 95% CI, 1.07-1.91 respectively); and multiple birth defects (adjusted risk ratio, 1.42; 95% CI, 1.03-1.94; and adjusted risk ratio, 1.47; 95% CI, 1.03-2.09, respectively).
Conclusion: Maternal delivery age is an important risk factor for all birth defects. Mothers and fathers who work as "cleaners and laborers and related workers" appear to have a higher risk of giving birth to children with chromosomal single birth defect and nonchromosomal single birth defect and multiple birth defects, respectively. Further in-depth study would be needed to confirm these observations.