Spontaneous abortions and reproductive selection mechanisms

Spontaneous abortions in hospitals were analysed from two sources-membership files of the Union of Rubber and Leather Workers (about 10000 women) and records of the personnel of a rubber factory (about 1600 women). Two frequencies of spontaneous abortions were calculated for each population analysed: rate (No spontaneous abortions x 100/No pregnancies) and ratio (No spontaneous abortions x 100/No births). The two frequencies were increased for all union members compared with all Finnish women. The frequencies, however, did not appreciably differ when the pregnancies occurred during union membership as compared with the pregnancies before or after membership. The frequency of spontaneous abortions was higher for the short-time union members than for those employed for longer periods, but the increased frequency did not correlate with union membership. The employees of a rubber factory had slightly fewer spontaneous abortions on average than the community population. The women employed in the rubber factory for three to 23 months were found to have appreciably higher frequencies of spontaneous abortions than the women employed for longer periods. The present study showed the feasibility of using cases of spontaneous abortions in hospitals in an occupational study with longitudinal employment data. Women with short periods ofemployment appeared to have more spontaneous abortions than those with longer periods of employment suggesting the presence of selection mechanisms, perhaps with some analogies to the "healthy worker effect" in occupational mortality studies. The presence of such selection mechanisms deserve serious consideration in occupational reproductive epidemiology. A survey on the chemicals currently used in the rubber industry identified some 500 entities, many with limited toxicological data. In its present technology, rubber work entails a considerable amount of manual activity that prevents total isolation of the work processes. Many years ago rubber work was associated with an increased risk of cancer in the workers2; this has been confirmed in several later investigations. 343 Female rubber workers have been reported as dying more frequently from lung cancer.5 Finnish rubber workers have excreted increased amounts of thioethers 14 and mutagenic compounds 15 in their urine. In the present study spontaneous abortions of rubber and leather workers were investigated. The workers were identified from two independent sources-the membership files of the Union of Received 15 June 1981 Accepted 22 March 1982 Rubber and Leather Workers and the records of the personnel of a rubber factory. All the spontaneous abortions in hospitals from 1973 to 1977 were identified from a computerised hospital discharge register. 16-18 As many types of selection mechanisms operate in reproductive performance as well as in female employment, attempts were made to unravel such mechanisms. Additionally, the rubber industry served as a model of a heavy and demanding employment for women, and special methodological problems of such a study population were presented. This paper provides evidence on the feasibility of relating hospital records on spontaneous abortions to data on employment provided by trade unions and by companies. Material and methods The Finnish National Board of Health maintains a 81 group.bmj.com on June 20, 2017 Published by http://oem.bmj.com/ Downloaded from