Spontaneous abortion: A prospective cohort study of younger women from the general population in Denmark. Validation, occurrence and risk determinants

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Abstract
Objective. To assess the occurrence of spontaneous abortion, comparing two different data sources. To estimate the rate of spontaneous abortion over a 2‐year period, and examine potential predictors of the risk for incident spontaneous abortion. Methods. We used interview data from a population‐based prospective cohort study comprising 11,088 women and data from a linkage of the cohort with the Hospital Discharge Register to compare spontaneous abortions as reported in the interview with those identified in the register. Based on interview data, we estimated the rate of spontaneous abortion during the two‐year follow‐up. Finally, risk determinants for incident spontaneous abortion were analyzed by means of logistic regression. Results. A total of 654 spontaneous abortions before enrolment in the study were reported by the women compared to 531 abortions found in the register. More than 80% of the spontaneous abortions identified from both sources were recorded in the same year. During follow‐up a total of 20.9% of pregnancies intended to be carried to term ended as a spontaneous abortion. In the risk factor analysis, we found that previous spontaneous abortion, being single, never having used oral contraceptives, and use of intrauterine device were associated with increased risk of subsequent spontaneous abortion. In addition, it was indicated that a short interpregnancy interval following a spontaneous abortion may confer an increased risk of abortion in the subsequent pregnancy. Conclusion. We found a high rate of spontaneous abortion in the present study and an acceptable agreement between information obtained by interview and register information. More than 25% of the spontaneous abortions were only reported by the women, and this could not be explained by erroneously reported induced abortions, and may be early, nonhospitalized abortions. We confirm that number of previous spontaneous abortions is a strong determinant, and our data may also indicate a role of previous contraceptive habits. A role of the length of interpregnancy interval in the risk of spontaneous abortion cannot be ruled out.