Physician cognition, metacognition and affect may have an impact upon the quality of clinical reasoning. The purpose of this study was to examine the relationship between measures of physician metacognition and affect and patient outcomes in obstetric practice. Reflective coping (RC), proactive coping, need for cognition (NFC), tolerance for ambiguity, state-trait anxiety and metacognitive awareness were assessed for obstetricians (n = 12) who provided intra-partum care to 4,149 women. Outcome measures included delivery mode and intrapartum asphyxia. Analysis was carried out using logistic regression and tree-based classification. Obstetricians with high RC scores were more likely to perform a caesarean section (OR 1.59, p < 0.0001), less likely undertake a mid-forceps or low forceps delivery (OR 0.41, p < 0.0001; OR 0.49, p < 0.0001), and more likely to supervise a spontaneous vaginal delivery (OR 1.17, p = 0.08). Obstetricians with high NFC scores were more likely to perform a caesarean section (OR 1.53, p = 0.03), more likely to undertake a vacuum delivery (OR 5.8, p = 0.001), less likely undertake a mid-forceps delivery (OR 0.45, p = 0.02) and less likely to supervise a spontaneous vaginal delivery (OR 0.47, p < 0.0001). Obstetricians high in trait anxiety were more likely to perform a mid forceps delivery (OR 2.49, p = 0.01) or a vacuum delivery (OR 5.08, p = 0.003), and less likely to supervise a spontaneous vaginal delivery (OR 0.38, p < 0.0001). NFC was negatively associated (OR 0.10, p < 0.001) and trait anxiety was positively associated with intrapartum asphyxia (p < 0.05, rho = 0.582). In summary, physician cognitive processes and affect have a significant impact on patient outcomes, particularly in situations where there is a higher level of clinical unpredictability.