The journey from conception to birth may be the most dangerous any of us will ever make, and that journey for twins is all the more hazardous.
When we think of identical twins, we conjure a special kind of closeness, a harmony that stems from growing together in the womb.
But it's not that way for all identical twins. Some are the agents of each others' deaths. Most parents, though, have no idea how dangerous their twin pregnancies can be.
Brittany and Chris Smith are young parents who quickly learned the dangers of having identical twins.
Brittany, 20, married her high school sweetheart, Chris. The couple has had quite a traumatic year together.
First, they lost their Mississippi home in Hurricane Katrina. Then, five months ago, their world turned upside down again when Brittany found out she was pregnant with twins. They already had a 2-year-old son and were not prepared for twins. Nevertheless, the Smiths said they were very excited to welcome the twins into their home.
But it quickly became obvious that something was wrong.
"I was probably about three weeks pregnant when I started bleeding and had to go to the emergency room. That's when I found out I was having twins -- they did an ultrasound at the hospital," Brittany said.
Dr. Anthony Johnson, a high-risk pregnancy specialist at the University of North Carolina Children's Hospital, has handled thousands of twin pregnancies and is one of only a handful of experts who specialize in what Brittany's identical twins have -- twin-to-twin transfusion syndrome, or TTTS.
TTTS is a deadly condition that affects only the fetuses of identical twins. They come from the same fertilized egg but share one placenta that connects them to their mother's blood supply. Each fetus fights the other to get enough blood to survive.
According to Johnson, 60 percent to 70 percent of the time both babies die. Doctors, knowing that anything could go wrong with Brittany's babies, performed ultrasound after ultrasound on her.
If nothing is done to correct the unequal blood flow between the twins, it's a death sentence for one or both of them.
The twin that's losing blood can be starved of the nutrients it needs to grow; the twin with too much blood can die from heart failure as it struggles to support its sibling.
The only hope of saving both twins' lives is a new laser surgery to correct the blood flow between the twins. But the surgery has to happen very early in the pregnancy, and it has to happen in the womb.
When Johnson learned that Brittany's twins had TTTS, he asked her to come in immediately for the laser surgery.
With TTTS, a single day can make the difference between life and death for twins.
Johnson performs the laser procedure on fetuses that are so tiny they could fit in the palm of your hand. He explained the risks associated with the surgery to the Smiths. Both husband and wife wanted to go ahead with the procedure to try to keep both twins alive.
Since the operation is performed under local anaesthetic, Brittany remained awake the entire time.
The tip of the laser is less than one-fifth of an inch across and is attached to a tube. A screen allows the surgeons to see the tiny blood vessels they're aiming for. The doctor has to line up the laser before firing it and cauterizing the blood vessels closed.