Placental share and hemoglobin level in relation to birth weight in twin anemia-polycythemia sequence

- In normal MC twins, smaller twins often have a relative smaller placental share.
- In MC twins with TAPS, the anemic twin commonly occupies a larger placental share.
- In normal MC twins, birth weight is primarily associated with placental share.
- In MC twins with TAPS, fetal growth is determined by the net inter-twin transfusion.

IntroductionTwin anemia-polycythemia sequence (TAPS) is a newly described form of chronic twin transfusion. Previous observational studies noted a discordance between birth weight and individual placental share in TAPS. The purpose of this study was to investigate if fetal growth in monochorionic (MC) twins with TAPS is determined by placental share or by the net inter-twin blood transfusion.MethodsAll consecutive MC twin placentas of live-born twin pairs with and without TAPS examined at our center between June 2002 and February 2014 were included in this study. Hemoglobin (Hb) levels and individual placental share were evaluated at birth and correlated with birth weight share. We excluded MC twin pregnancies with twin-twin transfusion syndrome.ResultsA total of 270 MC twin pregnancies (TAPS group, n = 20; control group without TAPS, n = 250) were included in this study. Donors with TAPS had a lower birth weight than recipients in 90% (18/20) of cases, but a larger placental share in 65% (13/20) of cases. In the TAPS group, birth weight share was positively correlated with Hb share at birth (P < 0.01) but not with placental share (P = 0.54). In the control group without TAPS, birth weight share was strongly correlated with placental share (P < 0.01) but not with Hb share (P = 0.14).DiscussionA relatively larger placental share may enable the survival of the anemic twin in TAPS.ConclusionIn contrast with uncomplicated MC twins, fetal growth in MC twins with TAPS is determined primarily by the net inter-twin blood transfusion instead of placental share.