Paradoxical scalloped placenta with polyhydramnios in twin-twin transfusion syndrome

To describe the paradoxical occurrence of a scalloped placenta in the presence of polyhydramnios and assess its clinical significance in pregnancies complicated by twin-twin transfusion syndrome (TTTS) treated with laser therapy.

All patients who underwent laser therapy for TTTS between January 2003 and April 2004 were studied. TTTS was diagnosed and staged using the Quintero staging system. Normally the placenta is characterized by undulations of the fetal-placental surface visible by ultrasound (scalloped placenta). Patients with polyhydramnios will typically have a flattened, smooth, non-scalloped placenta. Operative tapes were reviewed and placental type assigned. Pre-, intra-, and postoperative characteristics of each study patient were obtained.

Fifteen of 120 patients (12.5%) were noted to have a scalloped placenta despite having polyhydramnios. There was no difference in mean gestational age at laser treatment (20.3+/-0.5 vs. 19.6+/-0.6 weeks, p=0.66) or in stage (p=0.07) between the two groups. The median and range preoperative maximum vertical pocket (MVP) in the recipient gestational sac differed significantly between the scalloped and non-scalloped patients (8.3 (8-12) vs. 10.5 (8-17), p=0.001). All 15 patients (100%) with a scalloped placenta required an amnioinfusion to expose all vascular anastomoses, while amnioinfusion was necessary in only 28 of the 105 patients (26.7%, p<0.001) with a non-scalloped placenta. Postoperative patent placental vessel was identified by surgical pathology in 6.7% of the scalloped placenta group vs. 1.9% of the non-scalloped placenta group (p=NS).

The definition of TTTS requires an MVP>or=8 cm in the recipient sac. Most patients will have a flattened placenta as a result of polyhydramnios in this sac. Our data show that a paradoxical scalloped placenta may still be present in approximately 12.5% of patients. This preoperative sonographic finding alerts to the potential need for amnioinfusion during laser therapy for TTTS to disclose all vessels to avoid missing placental vascular anastomoses. Amniocenteses should be avoided if possible in patients considering laser therapy to minimize the likelihood of iatrogenic placental scalloping.