Spontaneous abortions among factory workers. The importance of gravidity control

The purpose of this study were twofold. First to demonstrate the impact of gravidity control on the crude odds ratio (OR), the risk estimate of the total number of spontaneous abortions among all chemically exposed women in comparison with non-exposed women. Second, to discuss whether the increased proportion of higher gravidities among the exposed subjects did compensate for an increased risk of spontaneous abortion provoked by the chemical exposure. The study included 262 factory workers occupationally exposed predominantly to organic solvents and 241 reference women who were socially comparable and relatively free from chemical exposure of their work. The subjects are included in a historical prospective survey of 6 730 women representing 12 selected occupations in the Danish county of Funen. The data were collected by postal questionnaires in May 1980. The crude OR of spontaneous abortions among factory workers was significantly increased, but when controlled for gravidity, it was no longer statistically significant. The childbearing behaviour of the two groups of women was compared in a logistic regression analysis which suggested that the increased proportion of higher gravidities among the factory workers was not only due to a compensatory behaviour. A desire for more children among the factory workers, or a less careful use of contraception compared to the reference group might explain the findings. Consequently, gravidity should probably be controlled.