Summary.The aim of this study is to identify social preventive measures in an attempt to prevent pre‐term birth in pregnant women who work under strenuous conditions. A study carried out in 50 factories allowed us to gather data on 1168 pregnancies that occurred during 1 year and to study the modifications in working conditions now granted to pregnant women in many firms in France. We observed a significant relationship between ‘episodes of sick leave’ prescribed especially for fatigue (without any pathological reason) and a lower preterm birth rate. The potential benefit of rest‐periods, granted to pregnant women working in strenuous conditions, is di