STUDY QUESTION How are educational level, labor market attachment and income associated with receiving a first ART treatment in either the public or private healthcare sector among women in Denmark? SUMMARY ANSWER Higher educational level and income as well as labor market attachment were associated with higher probability of initiating ART treatment at public and private fertility clinics among women in Denmark. WHAT IS KNOWN ALREADY Infertility is common in populations worldwide, and the approach to this issue differs between societies and healthcare systems. In the public Danish healthcare system, ART treatment is free of charge, and the direct cost for patients is therefore low. In the private healthcare sector in Denmark, ART treatment is self-financed. There is limited knowledge about the association between socioeconomic factors and seeking ART treatment, although previous studies have indicated that higher socioeconomic status is associated with seeking ART treatment. STUDY DESIGN, SIZE, DURATION Women undergoing ART treatment during 1994-2016 registered in the Danish IVF register were individually linked with data from sociodemographic population registers using the Danish Personal Identification number. The study population consisted of 69 018 women treated with ART and 670 713 age-matched comparison women from the background population with no previous history of ART treatment. PARTICIPANTS/MATERIALS, SETTING, METHODS The women included in the analyses were aged 18-45 years. The associations between attained educational level, labor market attachment and income and receiving a first ART treatment attempt were investigated for women either initiating treatment in the public sector or in the private sector, respectively. Information on age and origin was included as potential confounders, and odds ratios (ORs) were estimated in logistic regression models. In addition, analyses were stratified by age group to investigate potential differences across the age span. MAIN RESULTS AND THE ROLE OF CHANCE Adjusted results showed increased odds of receiving a first ART treatment in either the public or private sector among women with a higher educational level. Furthermore, women in employment were more likely to receive a first ART treatment in the public or private sector compared to women outside the workforce. The odds of receiving a first ART treatment increased with increasing income level. Surprisingly, income level had a greater impact on the odds of receiving a first ART treatment in the public sector than in the private sector. Women in the highest income group had 10 times higher odds of receiving a first ART treatment in the public sector (OR: 10.53 95% CI: 10.13, 10.95) compared to women in the lowest income group. Sub-analyses in different age groups showed significant associations between ART treatment and income level and labor market attachment in all age groups. LIMITATIONS, REASONS FOR CAUTION Our study does not include non-ART treatments, as the national IVF register did not register these types of fertility treatments before 2007. WIDER IMPLICATIONS OF THE FINDINGS In Denmark, there is equal access to medically assisted reproduction treatment in the publicly funded healthcare system, and since there is no social inequality in the prevalence of infertility, social inequality in the use of ART treatment would not be expected as such.

However, our results show that social inequality is found for a first ART treatment attempt across publicly and privately funded ART treatment across the socioeconomic indicators, educational level, labor market attachment and income. STUDY FUNDING/COMPETING INTEREST(S) The funding for the establishment of the Danish National ART-Couple II Cohort (DANAC II Cohort) was obtained from the Rosa Ebba Hansen Foundation. The authors have no conflict of interest to declare.