Odds ratios (ORs) of OASIS in nulliparous women including women admitted for first vaginal delivery after a prior cesarean section after adjustments for age and risk factors for OASIS.

SES = socioeconomic status, a The ‘other’ group included entrepreneurs, students, retired, unemployed, housewives and unclassifiable cases.*The contribution of risk factors for OASIS to socioeconomic disparities in OASIS were measured by the percentage reduction in the odds ratio of each SES group compared to Model 2 by using formula (OR Model 2 – OR Model 3/4/5/6)/(OR Model 2 – 1).