Strengths and Limitations
Our study has all the limitations of a retrospective review, and it is possible that a few donor or recipient cases were mislabeled when the databases were generated; however, this should not affect the results of our study since DUAPI represents the absolute intertwin differences in UA PI. In addition, 6.7% (25/374) of TTTS cases were lost to follow-up to 30 days, but there were no significant differences in the proportion of lost to follow-up cases between the DUAPI groups (<0.4 and ≥0.4), which reduces the possibility of selection bias. Similarly, the proportion of double twin survival to 30 days was not different between TTTS cases included or excluded in the study based on DUAPI availability (67% vs. 68.6%; p=0.9), which should also reduce the risk of selection bias. Strengths of the study are the inclusion of consecutive patients at two large academic institutions, and the regression analyses performed, which was adjusted for important confounding variables such as gestational age at delivery, sFGR, placental location, size of the trocar, and Quintero staging among others.