How do physicians respond to new medical research?

What happens when the findings of a prominent medical study are overturned? Using a medical trial on breech births, we estimate the effect of the reversal of such a medical study on physician choices and infant health outcomes. Using the United States Birth Certificate Records from 1995 to 2010, we employ a difference‐in‐differences estimator for C‐sections, low Apgar, and low birth weight measures. We find that the reversal of a multi‐site, high profile, randomized control trial on the appropriate delivery of term breech births, the Term Breech Trial, led to a 15%–23% decline in C‐sections for such births at a time when the overall trend in C‐sections was rising. We find our largest estimated effects amongst traditionally disadvantaged groups (i.e., non‐white, and minimal education). However, we do not find that such a change in practice had significant impacts on infant health. Contrary to prior studies, we find that physicians updated their beliefs quickly, and do indeed adjust to new medical research, particularly young physicians, prior to mandatory policy or professional guidelines.