Temporal characteristics related to leave from work and pregnancy among mothers with congenitally malformed offspring.

The possible impact of occupational factors on the furtherance of congenital defects have been under study at our department for the past 4 years. The topic has assumed a special interest because of the importance of the issue involved, namely the search for a possibility to prevent teratogenesis, and partly because the applicable methods are different from those of "customary" epidemiology. In connection with a register-based, case-referent study utilizing supplementary information, acquired via questioning, of conditions at the mothers' work places, we analysed various time-related events in their pregnancy. We found that the groups compared differed from each other with regard to the correct timing of the birth, despite the fact that the distribution of the times of stopping work for various reasons were alike. Among mothers who were granted sick leave from work the diagnosis of anencephaly became less common close to the estimated date of delivery, and conversely for the diagnosis of hydrocephaly. The findings of the present study may suggest that the time of assignment for a statutory maternity leave be considered. Methodological issues in study design are also briefly discussed.