[Placental characteristics of twin-to-twin transfusion syndrome]

To explore the prevalence, number and size of anastomoses, placenta sharing and placental cord insertion in twin-to-twin transfusion syndrome (TTTS).

A total of 97 monochorionic placentas were collected from June 2013 to June 2014 during fetoscopic laser surgery or selective feticide. After eliminating 23 placentas of selective intrauterine growth restriction (sIUGR), 79 placents were analyzed. There were 24 placentas of TTTS and 32 placentas of normal monochorionic twins (McT) without complex twin preganancy. Placental sharing, placental cord insertion, angioarchitecture and diameter of vascular anastomosis were assessed by placental injection with colored dye and compared between TTTS and McT without complex twin preganancy.

(1) Arterio-arterial (AA) anastomoses were detected in 37.5% of TTTS placentas versus 75.0% in normal McT placentas (P<0.01). (2) The median number of AA anastomoses in TTTS group was significantly less than that in normal group (0.0 vs 1.0, P<0.01). And the median total diameter of AA anastomoses in TTTS group was significantly smaller than that in normal group (0.00 vs 2.25 mm, P<0.01). (3) The incidence of placentas with at least one cord non-central insertion (70.8% vs 62.5%, P>0.05), velamentous insertion (25.0% vs 6.3%, P>0.05) in TTTS and normal McT had no difference respectively. The placental territory discordance (PTD) had no difference between TTTS and normal McT (0.33 vs 0.22, P>0.05).

AA anastomosis occurs less frequently in TTTS placentas, supporting the concept of a protective role of AA anastomoses in TTTS. McT placentas without AA anastomosis have high risk for TTTS. The compensatory ablitiy of AA anastomosis may determine the time of TTTS onset. Non-central or velamentous cord insertion, placental sharing discordance are not risk factors for TTTS.