One false blast of the laser could injure both babies, tear through the placenta and cause the babies to bleed to death.
Brittany had to stay perfectly still when they fired the laser. Correct aim is difficult because the twins keep moving. The surgery is supposed to last about 30 minutes, but in Brittany's case, it went on for hours.
While sitting in the waiting room, Chris wondered what was taking so long.
"I thought something went wrong, something had happened to [either] baby or something had happened to her. I really didn't know what to think," he said.
Brittany said she also felt as if something was going wrong during the surgery.
The problem was the twins were positioned awkwardly. Worse, every time the doctor fired the laser, a small amount of blood leaked into the womb, clouding the fluid there and making it harder and harder for the surgeon to see. After 2½ hours, Johnson stopped operating.
Brittany was wheeled into the recovery room, where staff monitored her for the next 48 hours. Brittany slept, while her family waited to hear if the operation had been successful.
When she woke up, Johnson told Brittany there'd been some complications during the operation that caused a drop in the heart rate of one of the babies. They still didn't know if the operation had worked. Johnson told Brittany that Day 2 in recovery would be the most critical.
Thirty-six hours after the operation, Johnson discovered the laser surgery hadn't sealed enough of the blood vessels shared by the unborn twins. Johnson didn't believe he could make another attempt because the amniotic fluid was too cloudy.
"We do not want to subject Brittany to a procedure if we know it won't work. Almost like protecting the patient from itself, this is a bad disease," Johnson said.
Johnson had to then do the hardest part of his job. He had to tell the family the operation hadn't worked and that Brittany would lose at least one of her babies. It was an agonizing dilemma: wait and risk losing both babies or terminate one to save the other.
By morning, the decision had been taken out of their hands. There was stillness on one side of the uterus.
"There's no heartbeat in the larger fetus. There is no cardiac activity at all," Johnson said.
There was no heartbeat in the twin the Smiths had already named Isaac. But devastating as that news was, there was optimism for the surviving twin, Ian, who had the weaker heart.
"The heart looks good on the survivor and the blood flow on the cord said we have a good shot at this," Johnson said.
Johnson sent the family home to wait two more months for baby Ian to be born safely. The dead twin remained inside Brittany for those final months of the pregnancy.
It may seem strange, but since babies with TTTS always share one placenta and one amniotic sac, removing one twin would mean delivering the other. So the mother must carry the dead twin until its surviving sibling is ready to be born.
Ian was born just three weeks after they'd left Johnson's office -- 14 weeks premature. He was only 12 inches long, but because his heart was failing, doctors said they'd had no choice but to rush him into the world.
Brittany wasn't able to hold her own son until a week after his birth because he was too vulnerable to infection to touch.
"It was sad to see him hooked up to everything. Have IVs and cords going through his belly button and him being so small. But I was excited that he was fine," Brittany said.