Prenatal care ensures favorable results for maternal-fetal health and, to that end, it must be provided early, periodically, comprehensively and with high coverage. To find out the social determinants of prenatal care in women affiliated to the Mexican Institute of Social Security during 2014. Cross-sectional study where the association of social conditions, social support and family functioning with inadequate prenatal care was analyzed. A descriptive analysis was performed; hypothesis tests were used with chi-square (95% level of confidence). The prevalence ratio and Mann-Whitney's U-test were estimated to compare medians and logistic regression. Of the interviewed women, 58.1% had inadequate prenatal care, mainly associated with unplanned pregnancy, poor social support, low level of education and higher marginalization. Not having leaves of absence granted by employers was the main barrier in those women who did not attend health services. There is a need for strategies to be designed and implemented to enable understanding the interaction between different biological and social dimensions of the health-disease process and reduce health inequities that affect pregnant women, in order to achieve good prenatal care and to implement alternative models guaranteeing its efficiency. Copyright: © 2018 SecretarÍa de Salud.