The general aim of this thesis was to explore women's reactions to and experiences of fetal screening for Down's syndrome PS) by means of an ultrasound examination, including measurement of fetal nuchal translucency (NT). The effect of this screening on maternal worry about the baby's health was investigated, as well as reactions to a false positive test and interpretation of information about riskAlso, an instrument measuring worry during pregnancy, the Cambridge Worry Scale, was translated into Swedish and tested on a sample of pregnant women.A sub-sample of 2026 women was drawn from a larger randomised controlled trial including 39,572 women, which investigated medical outcomes of the new fetal screening policy. Of these women, 1030 were randomly allocated to the intervention group, and 996 to routine care. No statistically significant differences were found between the two groups regarding major worry about something being wrong with the baby, general anxiety and depressive symptoms m midpregnancy and two months postpartum.Twenty-four women who had received information about an increased risk according to NT were interviewed during pregnancy and after birth. Twenty of these women had false positive tests, and for 16 the risk was higher than expected considering their age. These women expressed major worry, and many said they chose to reject their pregnancy, to take "time out", while waiting for the results of fetal karyotyping. Two months after the birth, most of these women seemed to have overcome the stressful situation.In the intervention group of the above trial 796 women had a risk score for DS recorded in a clinical database. Of these women 620 said they had received information about the risk score, and 64 percent stated the figure almost correctly. The actual risk was associated with women's perception of the risk. Worry about the baby's health and depressive symptoms did not differ statistically between women who were at high risk (1:250 or higher) and at low risk. However, women who perceived that the risk was high were more worried about the baby's health and also seemed to have more depressive symptoms in mid-pregnancy compared with those who perceived the risk to be low. No differences were observed at two months after birth.The translated version of the Cambridge Worry Scale was tested on 200 Swedish pregnant women in Stockholm. The three main sources of worry were about the baby's health, giving birth and miscarriage. The internal- consistency reliability was 0.81 (Cronbach's alpha). Three items were added to the original scale to capture women's worry about the maternity services.In conclusion, the intervention with an early ultrasound examination including risk assessment for DS by measuring the NT did not affect maternal worry about the baby's health, general anxiety or depressive symptoms 'm mid-pregnancy or two months after birth. However, a false positive test could cause strong reactions of anxiety and rejection of the pregnancy for some weeks. Many had problems to recall and interpret a given risk score. An actual high risk score was not associated with major worry about the baby's health or depressive symptoms, whereas a woman's perception of being at high risk had such an association. The Swedish version of the Cambridge Worry Scale was considered to be useful and well suited for its purpose.