Socioeconomic status and fecundability in a Danish preconception cohort

STUDY QUESTION: To what extent is socioeconomic status (SES), as measured by educational attainment and household income, associated with fecundability in a cohort of Danish couples trying to conceive? SUMMARY ANSWER: In this preconception cohort, lower educational attainment and lower household income were associated with lower fecundability after adjusting for potential confounders. WHAT IS KNOWN ALREADY: Approximately 15% of couples are affected by infertility. Socioeconomic disparities in health are well established. However, little is known about socioeconomic disparity and its relation to fertility. STUDY DESIGN, SIZE, DURATION: This is a cohort study of Danish females aged 18-49 years who were trying to conceive between 2007 and 2021. Information was collected via baseline and bi-monthly follow-up questionnaires for 12 months or until reported pregnancy. PARTICIPANTS/MATERIALS, SETTING, METHODS: Overall, 10 475 participants contributed 38 629 menstrual cycles and 6554 pregnancies during a maximum of 12 cycles of follow-up. We used proportional probabilities regression models to estimate fecundability ratios (FRs) and 95% CIs. MAIN RESULTS AND THE ROLE OF CHANCE: Compared with upper tertiary education (highest level), fecundability was substantially lower for primary and secondary school (FR: 0.73, 95% CI: 0.62-0.85), upper secondary school (FR: 0.89, 95% CI: 0.79-1.00), vocational education (FR: 0.81, 95% CI: 0.75-0.89), and lower tertiary education (FR: 0.87, 95% CI: 0.80-0.95), but not for middle tertiary education (FR: 0.98, 95% CI: 0.93-1.03). Compared with a monthly household income of >65 000 DKK, fecundability was lower for household income <25 000 DKK (FR: 0.78, 95% CI: 0.72-0.85), 25 000-39 000 DKK (FR: 0.88, 95% CI: 0.82-0.94), and 40 000-65 000 DKK (FR: 0.94, 95% CI: 0.88-0.99). The results did not change appreciably after adjustment for potential confounders. LIMITATIONS, REASONS FOR CAUTION: We used educational attainment and household income as indicators of SES. However, SES is a complex concept, and these indicators may not reflect all aspects of SES. The study recruited couples planning to conceive, including the full spectrum of fertility from less fertile to highly fertile individuals. Our results may generalize to most couples who are trying to conceive. WIDER IMPLICATIONS OF THE FINDINGS: Our results are consistent with the literature indicating well-documented inequities in health across socioeconomic groups. The associations for income were surprisingly strong considering the Danish welfare state. These results indicate that the redistributive welfare system in Denmark does not suffice to eradicate inequities in reproductive health. STUDY FUNDING/COMPETING INTEREST(S): The study was supported by the Department of Clinical Epidemiology, Aarhus University and Aarhus University Hospital, and the National Institute of Child Health and Human Development (RO1-HD086742, R21-HD050264, and R01-HD060680). The authors declare no conflict of interest. TRIAL REGISTRATION NUMBER: N/A.