LAUSR

BACKGROUND Medical guidelines recommend vaginal delivery for low-risk twin pregnancies because cesareans increase the probability of maternal morbidity and mortality. Yet, vaginal delivery rates for twins are considerably lower than for comparable singletons. One explanation for this disparity argues that greater risk associated with twins warrants increased surgical intervention. An alternative explanation is that twin deliveries are more likely to deviate from protocols that advise vaginal birth. METHODS Using the 2017 Natality Detail File (N = 3,197,401), we measured alignment of vaginal birth and trial of labor (TOL) with the American College of Obstetricians and Gynecologists' guidelines for twin and singleton no-indicated-risk births. We calculated predicted probabilities for the population and by maternal race/ethnicity to assess whether low rates of vaginal births among twins are explained by associated risk factors, or by deviations from recommended delivery methods. RESULTS Overall, 31.2% of twins were born vaginally compared with 79.4% of singletons. Controlling for indicated risks, the predicted probability of vaginal birth for twins was 0.49 and 0.85 for singletons. The predicted probability of TOL for twins was 0.18 and 0.47 for singletons. Maternal race/ethnicity was only weakly associated with mode of delivery. These findings indicate that no-indicated-risk twin pregnancies, across maternal racial/ethnic categories, have lower probabilities of vaginal birth and TOL than would be expected with widespread adherence to current guidelines. CONCLUSIONS Given the life-threatening consequences that may result from unnecessary surgical procedures, our findings highlight the need for further research to illuminate medical and nonmedical mechanisms driving nonadherence to clinical guidelines for twin births.