Potassium chloride is reported to kill both monochorionic twins after injection into only one. In this study, two women undergoing in vitro fertilization and embryo transfer were pregnant with triplets containing monochorionic twinning, which were detected by ultrasound with the presence of a "twin-peak" sign. Instead of potassium chloride, intrathoracic injection of amniotic fluid was employed to sacrifice one of the monochorionic fetuses in dichorionic triplets. Our aim was to sacrifice one of the monochorionic twins in order to prevent adverse perinatal outcomes and to avoid the harmful effect of potassium chloride on monochorionic cotwins. One twin pregnancy was terminated with preterm premature rupture of membranes at 25 weeks of gestation. In the second one, two healthy babies were delivered by cesarean section at 36 weeks of gestation. The female baby weighed 2100 gm and the male baby 2600 gm, respectively. Intrathoracic injection of amniotic fluid to create a tamponade is an alternative management for fetal reduction.