Meet the fetal surgeon forging CRISPR’s next frontier: curing diseases in the womb

SAN FRANCISCO — Outside, the August sun wasn’t yet visible through the thick folds of fog blanketing the San Francisco skyline. Its warmth did not reach the operating room tucked into the sprawling Parnassus Heights hospital complex. In there, the light was all cold and blue fluorescence washing over the sea of scrub caps huddled around an anesthetized young woman on a gurney. From one corner of the crowded room, a medical student named Tippi MacKenzie watched, eyes widening, as the woman’s uterus was gently lifted out of her open abdomen and an incision was made to expose the legs and backside of the fetus inside.

At 23 weeks, it was barely the size of a mango, made even smaller by the massive, glistening purple tumor protruding from its tailbone. As the doctors began the painstaking process of removing the mass — an orchestrated flurry of fingers tying knots, scalpels slicing flesh, cautery pens searing blood vessels shut — the room grew thick with anticipation. Sacrococcygeal teratomas weren’t usually cancerous, but these kinds of tumors steal the fetus’ blood supply...