Ultrasound waves may offer a new tool for splitting abnormal blood vessels in the placenta that affect some twin pregnancies, a new study shows in sheep. With further development, the technique may offer a less invasive and potentially safer alternative for treating twin-twin transfusion syndrome (TTTS), a rare but lethal complication of some pregnancies in which identical twins share a placenta. In this disorder, abnormal blood vessel connections form between twin fetuses, resulting in unequal sharing of the placental blood supply. Current invasive laser surgery for destroying the connecting vessels is often ineffective and risky, and therefore reserved for severe cases. Caroline Shaw and colleagues sought to use high-intensity focused ultrasound to ablate placental blood vessels in healthy pregnant sheep. When placed on the uterine surface, the ultrasound successfully occluded placental vessels with few complications. Both mother and baby sheep were unharmed, and blood flow to the fetal brain remained normal. The findings suggest that the ultrasound technique may be further adapted to treat TTTS and potentially related pregnancy disorders.