Clinical decisions made in the delivery setting as to whether to employ vaginal delivery or cesarean section are often made under high pressure, and with great uncertainty, and have serious consequences for mother and baby. Now, a new study of electronic health records of 86,000 deliveries, conducted by the University of Massachusetts Amherst, suggests that if their prior patient had complications in one delivery mode, a physician will be more likely to switch to the other, and likely inappropriate, delivery mode for the subsequent patient, regardless of whether it is warranted for that patient’s indications. The research says this implies that physicians may sometimes rely not on scientific evidence, but on heuristics — simplified decision rules to aid complex decision-making — to determine their course of action, ultimately with sub-optimal effects on patient health.