Objective: To describe the incidence of clinical miscarriage and to investigate the factors influencing the occurrence of clinical miscarriage.
Design: Prospective study with both cross-sectional and longitudinal comparisons.
Setting: City of Göteborg, Sweden.
Population: Population-based study in cohorts of 19-year-old women followed longitudinally.
Main outcome measures: Incidence of miscarriage and pregnancy outcome.
Material and methods: A postal questionnaire was sent to women born in 1962 and resident in the city of Göteborg in 1981 (n = 656) regarding pregnancy outcome, clinical miscarriage and other reproductive health factors. Responders in 1981 were contacted again and requested to answer a similar questionnaire every fifth year up to 2001. The same process was repeated in 1991 with women born in 1972 (n = 780) with follow up of these responders in 1996 and 2001. A third cohort of 19-year-old women born in 1982 (n = 666) was interviewed in 2001. The self-reported pregnancy data were verified from hospital files.
Results: Complete data were available for 341 women born in 1962 and assessed up to the age of 39 years (ever pregnant, n = 320, 94%). There were in total 887 pregnancies (live birth, n = 590, 67%; miscarriage, n = 108, 12%; legal abortion, n = 173, 20% and ectopic pregnancy, n = 16, 2%). Of the 320 'ever pregnant' women, 80 women (25%) had experienced a miscarriage. 76.3% had experienced one miscarriage, 16.3% had two miscarriages and 7.4% had three or more miscarriages. The clinical miscarriage rates in women at different ages were as follows: 20-24 years 13.5%, 25-29 years 12.3%, 30-34 years 10.3% and 35-39 years 17.5%. The corresponding miscarriage rate in the 1972 cohort followed from 19 to 29 years of age was 11%, and in the 1982 cohort assessed at 19 years of age, the miscarriage rate was 9%. No risk factor for miscarriage could be reliably identified.
Conclusions: Clinical miscarriage constituted 12% of all pregnancies, and one in four women who had been pregnant up to 39 years of age had experienced a miscarriage. Three or more miscarriages were experienced by 7.4%. The occurrence of a miscarriage was not influenced by the order of the pregnancy.