Introduction Socioeconomic conditions are rarely considered in the epidemiology of subfertility.

Objectives Access the effect of current and past socioeconomic conditions on the occurrence of subfertility in women with a successful pregnancy.

Methods Women were recruited in 2005/6 for Geração XXI, a Portuguese birth cohort. Personal interviews were conducted to collect socio-demographic and pregnancy-related data. Life-time subfertility was self-reported and defined as trying to conceive for more than 1 year with no success. Education, income, working condition and marital status were proxy indicators of social class. The childhood circumstances of the women were accessed by parents' education and amenities at age 12. The analysis considered 7916 mothers. Logistic regression models were fitted to estimate the odds (OR) of being subfertile according socioeconomic circumstances, stratified by number of previous pregnancies (1 vs >1) and age (<30 vs ≥30 years).

Results Subfertility was reported by 9.1% of the women (n=719). Prevalence was 8.7% among primigravidae and 9.5% in multigravidae (84% of the multigravidae were multipara). Almost 2/3 sought for medical help. Among young primigravidae, subfertility decreased with education (>12 vs ≤6 years: OR 0.20 95% CI 0.11 to 0.39), and was lower among single (OR 0.27 95% CI 0.12 to 0.59) and smokers (OR 0.60; 95% CI 0.40 to 0.94). Only education presented a significant association with subfertility in older primigravidae. Within multigravidae higher education increased the odds. Maternal childhood conditions were no longer significant after adjustment for current social circumstances.

Conclusions Age and the number of previous births modified the effect of social conditions on subfertility which was stronger among younger and primigravidae women.