In this study 242 nulliparous pregnant women completed standardized psychometric questionnaires and semi-structured interviews in the latter half of pregnancy and again 4-6 weeks postpartum. Discriminant function analysis revealed that the use of operative obstetric interventions was measurably influenced by psychosocial factors. Privately insured women were significantly more likely to experience instrumentally assisted (relative risk = 1.53, 95% CI: 1.05, 2.25) and Caesarean (relative risk = 1.91, 95% CI: 1.05, 3.46) deliveries than those receiving care in the public hospital system. The likelihood of experiencing these procedures was increased further among those who in late pregnancy were thinking clearly, had high self-esteem, mature means of dealing with anxiety, were confident in their knowledge of childbirth procedures and in secure partnerships with highly educated men. There was no evidence that either elevated anxiety or abnormalities of personality contributed to obstetric outcome. These findings indicate that obstetric decision-making is significantly influenced by patient personality and socioeconomic circumstances. In particular, they suggest that fear of malpractice litigation, physician convenience factors and the response of obstetricians to assured, well pregnancy-educated pregnant women may be influencing the use of operative intervention in delivery.