The literature indicates a high percentage of sick leave during pregnancy in the past 10 years. In the Nordic countries 30-50 percent of pregnant women on the labour market are on sick leave during pregnancy. There is no indication that the increased frequency is due to decreased health amongst pregnant women, but it may be a consequence of an increase in working women. Pregnancy means additional strain to the double tasks that many working women experience. A few references indicate that sick leave is most common among women working full time and women, who have previously given birth. Sick leave may cover up for increasingly poor working environments or social problems, but may also reflect changes in standards, legislation or role performance. It is advisable to follow pregnant women on sick leave closely in order to avoid expulsion from the labour market. Pregnancy-related sick leave seems to be multifactorial, which should lead to caution concerning conclusions on the relative influence of different factors on sick leave during pregnancy.