Parental occupation and preterm births: a nationwide epidemiological study in Sweden.

The hypothesis was that some occupations could lead to preterm birth (PTB) because of potential exposures to various agents. The objective in this nationwide follow-up study was to analyse the association between PTB and parental occupational groups, controlling for potential confounders. Data from the Swedish Medical Birth Register, in which all children born in Sweden from 1990 onward are registered with their parents, were linked to census data. Inclusion criteria for the study population were employment (both women and men) and age >20 years (women). There were 816,743 first singleton live births from 1990 to 2004, of whom 43,956 were PTBs. A total of 7659 of the 43,956 PTBs were very PTBs. Odds ratios (ORs) with 95% confidence intervals were calculated separately for mothers and fathers to estimate the odds of PTB and very PTB in 51 occupational groups (reference groups: mothers or fathers who were 'Technical, science research-related workers and physicians') and by family income level. Women and men with low family incomes had increased ORs of PTB and very PTB. Significantly increased ORs of PTB (including very PTB) were found in four maternal and nine paternal occupational groups after accounting for family income, geographic region of residence, civil status, smoking habits, maternal age at infant's birth and period of birth. Further studies should examine specific agents in those parental occupations that were associated with increased odds of PTB and very PTB.