["to assess the association between non-clinical factors and the incidence of caesarean section (CS); to estimate the effect of a prenatal instructor's presence during childbirth on birth outcome (vaginal or CS).", 'cross-sectional study from a register of women who attended prenatal classes. Multivariate logistic regression was used to measure the effects of each variable on whether the birth was vaginal or CS.', 'Mexico City, Mexico.', '992 births to 847 women from the register of the Birth Education Centre (CEPAPAR) between 1987 and 2000.', 'the incidence of CS was 33%. The most commonly reported (by the women) reason for performing a CS was dystocia (53%). Most women were middle or upper-middle class professionals, and 85% of the women gave birth in private institutions. Odds of having a CS were higher among women who gave birth in a large hospital, women who were over 25 years of age, primigravidae, and women who were not supported by a prenatal instructor during childbirth.'] Is support from a prenatal instructor during childbirth associated with reduced rates of caesarean section in a Mexican study?