At a clinic in Salt Lake City, the ultrasound technician moved the transducer in slow circles over Erin Herrin’s abdomen. Erin, 20 and already the mother of a two-year-old girl, was 18 weeks into her second pregnancy.
“Wow! Do you see that?” said the sonographer, zeroing in on a pair of small, fluttering images. “Two hearts! Congratulations-you’re having twins.” Erin wasn’t entirely surprised; she’d felt extra kicks this time, though her obstetrician had heard only one heartbeat during earlier tests. She grinned at her husband, Jake, 21, who stood holding her hand.
Then the sonographer stopped the exam. “Just a minute,” she said. “I want the radiologist to take a look at this.”
The Herrins waited anxiously as the specialist arrived and studied the ultrasound scans. “It looks like you’re having conjoined twin girls,” he said at last, his tone apologetic. “I really can’t tell you much more than that.” He scheduled an appointment for them to meet with a perinatologist the following Monday—four long days away.
On the drive home, Erin, a homemaker, ran down a preliminary list of questions: Where are the babies connected? Can they be separated? Will they ever have a normal life? Are they even going to live? Jake, a computer network manager, tried to reassure her. “Let’s not panic,” he said. “Maybe they’re just attached by a bit of skin and there’s a way to fix it.”
As it turned out, the twins shared a great deal more than that. If they made it to term, their only hope of independence—from each other as well as from their caregivers—would be a surgical procedure of almost unimaginable complexity. In fact, it would be the first operation of its kind.
When they got home from the clinic that fall day in 2001, Jake and Erin looked up conjoined twins online. They learned that in 1 out of 100,000 pregnancies, a fertilized egg fails to divide fully into identical twins, leaving two fetuses joined at some point along their bodies. For unknown reasons, about 70 percent are girls, and in most cases, their shared internal organs are severely deformed. Up to 60 percent of conjoined twins are stillborn; of those who survive birth, 35 percent live only one day. The overall survival rate is 25 percent.
The first successful separation took place in Switzerland in 1689—a simple case involving superficially joined twins. But such operations remained almost unheard-of until surgical techniques improved in the 1950s. Since then, a few dozen sets of twins worldwide have been separated. Survival rates vary depending on where the twins are connected, from 82 percent for those joined only at the abdomen to zero for those who share a heart.