IPSILON ZONE

The ipsilon zone is the junction between the three interfetal membranes in triplet pregnancies. Its characteristic prenatal ultrasonographic appearance is a Y-shaped or ipsilon zone (1).

The three membranes are best studied and their thickness compared at this junctional area. The ipsilon zone is not present in all triamniotic pregnancies as the sacs may be parallel to each other. Chorionicity must be determined by evaluating the intertwin membrane-placental junctions.

REFERENCES

1. Sepulveda W, Sebire NJ, Odibo A et.al. Prenatal determination of chorionicity in triplet pregnancy by ultrasonographic examination of the ipsilon zone. Obstet Gynecol 1996;88:855-858.