Adverse perinatal outcome of twin pregnancies according to chorionicity: Review of the literature

Twin gestations are at significant increased risk for adverse perinatal out come. As a result, although prospective randomized data is lacking, increas ed fetal surveillance has been advocated for twins. Growth concordance is c onsidered a reassuring sign in twins and conversely, discordancy to possibl y reflect a hostile intrauterine environment at least to the smaller twin. Consequently, increased surveillance of discordant twins is commonly practi ced. Monochorionic twins are at further risk for type-specific perinatal co mplications, for example, twin-twin transfusion syndrome. Recently, precise first-trimester depiction of chorionicity has enabled early antepartum str atification of twin gestations according to chorionicity, in comparison wit h previous later (mid- and third-trimester) ultrasonographic diagnosis of c horionicity. This immediately leads to the question whether antenatal testi ng of twins should differ according to chorionicity? Review of the literatu re supports that despite the existence of complications unique to monochori onic twin gestations, dichorionic twins sustain an increased risk of advers e perinatal outcome (such as fetal growth restriction) in comparison with s ingletons, and that close antenatal fetal surveillance of twins should be p erformed, irrespective of chorionicity.