Very early twin-to-twin transfusion syndrome and discordant activation of the renin-angiotensin system.

We present evidence of a first-trimester discordant renin-angiotensin system (RAS) response and structural abnormalities of the kidneys in twins with twin-to-twin transfusion syndrome (TTTS). A dark red fetus and a pale fetus were spontaneously delivered at 13.5 weeks of gestation following a double intra-uterine death. Pathological examination confirmed the placentation as monochorionic, with arteriovenous anastomoses on the chorionic plate. The donor twin had a normal heart and mildly hypoplastic kidneys, and the recipient twin had cardiomegaly and hypertrophic kidneys. Immunohistochemical analysis of the kidneys showed secretion of renin occurring in the donor but not in the recipient twin, more intense expression of angiotensin II receptor type 1 in the donor, and modifications of renal architectures in both twins. Renin protein appeared qualitatively higher in the placental territory of the recipient compared to that of donor. These findings indicate that hemodynamic discordance caused by vascular anastomoses may lead to serious physiologic and organic consequences as early as the first trimester. To our knowledge, this case presents the earliest first-trimester TTTS confirmed by a complete anatomopathological examination and is the first TTTS case to show a first-trimester discordant RAS response confirmed by immunohistochemistry.