Male factors and socioeconomic indicators correlate with the risk of spontaneous abortion

No less than 10% of clinically recognised pregnancies end as spontaneous abortions and the recurrence risk is high. Due to lack of data and appropriate study design only little is known about preventable causes of miscarriage. The aim of this study was to estimate the effect of paternal and environmental factors by studying reproductive histories in population based cohorts. We based the study upon two cohorts. The 'abortion cohort' consisted of 55 259 women who had a hospitalised spontaneous abortion in Denmark between 1980 and 1992 and who had a subsequent non-terminated pregnancy. The 'birth cohort'was based upon a 5% random sample of all women who in the same time period gave birth and subsequently had a non-terminated pregnancy (11 269 women). Data on change of partner, residence, mother's social status or occupation between the two pregnancies were linked to these two cohorts using the personal identification numbers and information stored in several population registers. Change of partner reduced the recurrence risk of spontaneous abortion substantially (OR = 0.59; 95 CI 0.52-0.67), but also changes in social status or job reduced the recurrence risk significantly. Changing the municipality of residence to a low risk area (based upon the geographical distribution of spontaneous abortions) reduced the risk of spontaneous abortion in both cohorts. A paternal effect on the recurrence risk of spontaneous abortion cannot be ruled out but environmental factors also play a role.