The Northwestern Twin Chorionicity Study: I. Discordant inflammatory findings that are related to chorionicity in presenting versus nonpresenting twins.

OBJECTIVE: The purpose of this study was to evaluate the association between chorionicity and discordant chorioamnionitis and funisitis in twin gestations. STUDY DESIGN: This was a retrospective analysis of 1156 twin placentas with a standardized diagnosis of chorionicity, chorioamnionitis, and funisitis for comparison between presenting and nonpresenting twins with dichorionic-separate, dichorionic-fused, and monochorionic placentas. RESULTS: Frequencies of chorioamnionitis in the nonpresenting twin were significantly lower in dichorionic placentas (odds ratio, 0.4; 95% CI, 0.3, 0.6, in dichorionic-separate placentas; odds ratio, 0.5; 95% CI, 0.3, 0.8, in dichorionic-fused placentas) compared with monochorionic placentas. The frequency of advanced inflammation (ie, chorioamnionitis with funisitis) was significantly lower in the nonpresenting twin than in the presenting twin, but only in dichorionic-separate placentas (odds ratio, 0.2; 95% CI, 0.1, 0.4). CONCLUSION: Dichorionic placentas confer significant protection against the spread of chorioamnionitis from the presenting to the nonpresenting gestational sac. In the more advanced process that involves the umbilical cord, only the subset of separate dichorionic placentas confers this protective effect against the spread of inflammation.