Background Despite the realized importance of unsafe abortion as a global health problem, reliable data are difficult to obtain, especially in countries where abortion is illegal. Estimates for most developing countries are based on limited and incomplete sources of data. In Mexico, studies have been undertaken to improve estimates of induced abortion but the determinants of unsafe abortion have not been explored. Methods We analysed data from the 2006 Mexican National Demographic Survey. The sample comprises 14 859 reported pregnancies in women between 15 and 55 years old, of which 966 report having had an abortion in the 5 years preceding the survey. We use logistic regression to explore the relationship between unsafe abortion and various socio-economic and demographic characteristics. Findings We estimate that 44% of abortions have been induced and 16.5% of those were unsafe. We find three variables to be positively and significantly associated with the probability of having an induced abortion: (1) whether the woman reported that the pregnancy was mistimed (OR = 4.5, 95% CI = 1.95-10.95); (2) whether the woman reported that the pregnancy was unwanted (OR = 2.86, 95% CI = −1.40-5.88); and (3) if the woman had three or more children at the time of the abortion (OR = 3.73, 95% CI = 1.20-11.65). Inglés

There is a steep socio-economic gradient in the probability of having an unsafe abortion: poorer women are more likely to have an unsafe abortion than richer women (OR = 2.48, 95% CI = 1.09-5.63); women with 6-9 years of education (OR = 0.30, 95% CI = 0.11-0.81) and with more than 13 years of education are less likely to have an unsafe abortion (OR = 0.065, 95% CI = 0.01-0.43), and women with indigenous origin are more likely to have an unsafe abortion (OR = 5.44, 95% CI = 1.91-15.51). Thus, the probability for poor women with less than 5 years of education and indigenous origin is nine times higher compared with rich, educated and not indigenous women. We also find marked geographical inequities as women living in the poorest states have a higher risk of having an unsafe abortion. Interpretation This analysis has explored the determinants of unsafe abortion and has demonstrated that there are large socio-economic and geographical inequities in unsafe abortions in Mexico. Further efforts are required to improve the measurement and monitoring of trends in unsafe abortions in developing countries. Inglés