Physical work load, fetal development and course of pregnancy.

The effects of physical work load during pregnancy were analyzed in connection with a nationwide case-referent study that screened for associations between selected structural malformations and occupational exposures. The strain of the occupational activities of 1475 mothers of malformed infants and an equal number of mothers of noncase babies was assessed from a description of the work tasks by an expert using a standardized method reflecting energy expenditure. The noncase mothers' experience revealed a relation between physical load and growth retardation that has also been suggested by other epidemiologic studies. No relation was found between an increase in mean physical load and the occurrence of threatened abortion; yet work involving much standing had an increased risk. Mothers whose work included occasional high physical loads had more pregnancy-induced hypertension. The data showed unexpected associations between physical load and structural malformations.