Spontaneous abortions in Ontario, 1979 to 1984

Hospital data may be used to estimate the frequency of hospital admission for spontaneous abortion (miscarriage) in Ontario. Although many episodes of spontaneous abortion will be missed, especially those occurring early in gestation, these estimates can be used to identify fluctuations in the provincial average. Hospital Medical Records Institute (HMRI) provided data on hospital admissions for all hospitals in Ontario. Using these records, provincial admissions for spontaneous abortion (ICD 9 codes 632, 634 and 637) were analyzed for the period 1979 to 1984. Miscarriages occurring under 20 weeks were calculated as a percentage of total reported pregnancies, which included livebirths, stillbirths, and induced abortions. The miscarriage rate was steady throughout the period of observation, ranging from 6.8% to 7.2% and was observed to vary with maternal age and county of residence. Several Ontario counties consistently experienced high rates of spontaneous abortion for the years 1980 to 1984 inclusive. Possible reasons for these observations are discussed and suggestions for further investigations are proposed.