Placental Characteristics in Growth-discordant Monochorionic Twins: a Matched Case-control Study

Objective: To compare the placental characteristics in monochorionic (MC) twin pregnancies with and without birth weight discordance (BWD).

Methods: We performed a matched case-control study to compare the placental characteristics of MC placentas from pregnancies with BWD (≥25%) (n = 47) with a control group of MC placentas without BWD (n = 47), matched for gestational age at birth. Placental sharing, angioarchitecture and diameter of the arterio-arterial (AA) anastomosis were assessed by placental injection with colored dye.

Results: The rate of velamentous cord insertion in MC placentas with and without BWD was 30% (28/94) and 16% (15/94), respectively (p = 0.036). Placental sharing discordance in MC placentas with and without BWD was 36% and 17%, respectively (p < 0.001). The mean diameter of the AA anastomosis in MC placentas with and without BWD was 2.2 mm and 1.8 mm, respectively (p = 0.024).

Conclusion: MC placentas from growth-discordant twins are more unequally shared, have a higher rate of velamentous cord insertions and larger diameter of AA anastomosis compared to gestational age matched controls.