To investigate the relationship between different indicators of socioeconomic position and the risk of spontaneous abortion.
All first time participants, a total of 89 829 pregnant women, enrolled in the Danish National Birth Cohort were included in the present study. Overall, 4062 pregnancies ended in spontaneous abortion. Information on education, income and labour market attachment in the year before pregnancy was drawn from national registers.
Main outcome measure
Spontaneous abortion, that is, fetal death within the first 22 weeks of pregnancy, was the outcome of interest. The authors estimated HRs of spontaneous abortion using Cox regression analysis with gestational age as the underlying time scale.
Women with <10 years of education had an elevated risk of spontaneous abortion when compared with women with >12 years of education (HR 1.19 (95% CI 1.05 to 1.34)). The HR estimates for the four lowest income quintiles were all increased (HRs between 1.09 and 1.15) as compared with the upper quintile but did not differ considerably from each other. In general, no statistically significant association was found between labour market attachment and the risk of spontaneous abortion; however, the group of women on disability pension had an increased HR of spontaneous abortion when compared with women who were employed (HR 1.32 (95% CI 0.82 to 2.13)).
Educational level and income were inversely associated with the risk of spontaneous abortion. As these factors most likely are non-causally related to spontaneous abortion, the findings indicate that factors related to social position, probably of the environmental and behavioural type, may affect spontaneous abortion risk. The study highlights the need for studies addressing such exposures in order to prevent spontaneous abortions.
The focus of the study was to investigate the relationship between different indicators of socioeconomic position and the risk of spontaneous abortion, with the prospect of examining whether a proportion of spontaneous abortions are preventable.
Women of lower educational status have an elevated risk of spontaneous abortion, and women in the highest income quintile have lower risk of spontaneous abortion than those in the lower quintiles.
The socially patterned risk indicates that a proportion of spontaneous abortions may be preventable and that factors related to social position, probably of the environmental and behavioural type, may affect spontaneous abortion risk.
Strengths and limitations of this study
The present study is based upon a large population and a considerable number of spontaneous abortions, which offers a good foundation to examine the association between different indicators of socioeconomic position and spontaneous abortion.
The study design is prospective and therefore the decision whether to participate or not does not depend upon the outcome of the pregnancy.
To study spontaneous abortion is difficult since a great part of spontaneous abortions happen very early in the pregnancy period—many even before the women themselves know that they are pregnant—which is why we are restricted from being able to conclude anything about the association between socioeconomic position and the very early spontaneous abortions.