Evidence of early placental vascular anastomosis during selective embryo reduction in monozygotic twins.

Objective: To describe selective embryo reduction of two triplet pregnancies with a monozygotic twin.

Design: Case reports.

Setting: Infertility unit of a Department of Obstetrics and Gynecology.

Patient(s): Two patients treated with IVF-ET who had triplet pregnancies.

Intervention(s): Selective embryo reduction of monozygotic twins.

Main Outcome Measure(s): Fetal heart beat.

Result(s): During intracardiac injection of potassium chloride plus midazolam in one of the monozygotic twin fetuses, we observed an immediate diminution of the cardiac pulse rate of the second twin. This phenomenon was observed in both patients.

Conclusion(s): These observations clearly indicate the presence of vascular anastomosis between the two fetuses of these monozygotic twins. Thus, use of toxic substance to reduce one of the two fetuses of a monozygotic twin pregnancy is contraindicated. In cases of triplets that include a monozygotic twin, it is safest to interrupt the evolution of the twin if selective reduction is desired.