It's a condition that kills more children in their mothers' wombs than SIDS does in their first year of life, but you've probably haven't heard of it.
An East Tennessee family quickly for up to speed and is handling a diagnosis of Twin-to-Twin Transfusion Syndrome, or TTTS.
Courtney Crouse of Lenoir City was at Fort Sanders Regional Medical Center in Knoxville for her 18 week check up to find out the sex of her twins.
"That's when they said you're having girls. And then they said but you have twin to twin. And I just lost it," she remembered.
The next morning, Crouse left her two toddlers in Lenoir City with her husband, Stephen, and boarded a plane to Houston with her mother, Stacey Allen.
"They told me there were a few options we could do, none in Tennessee, I had to go to Texas," Crouse said.
She learned that TTTS is an imbalance between identical twins sharing a placenta that is usually fatal for the twins if untreated.
"One baby has too much blood. the other baby doesn't have enough," Karen Moise, RN, said. She is the Fetal Intervention Coordinator at Texas Children's Fetal Center.
That's where a thin tube with a camera was inserted into Courtney Crouse's womb where it allowed doctors to see vessels connecting the twins.
The solution was separation, achieved with laser ablation.
"We use laser energy to use heat to seal those vessels closed. My colleagues like to use the term spot weld. And what we do for all intents and purposes is we create two placentas, we separate them," Dr. Anthony Johnson of Texas Children's Fetal Center explained.
Stacey Allen said of the experience in Houston, "We went out there fully expecting that she might be able to save one baby. We left there with the expectation that both were going to be ok."
Crouse plans to deliver her babies at Fort Sanders in Knoxville. They're due in February but are expected to arrive early.
"They think they're going to be born around 33 or 34 weeks and probably about 3 pounds apiece," she said.
She looks forward to meeting the twins that so far she's seen only in ultrasound pictures.
"There's her head and her arm is right there," she said, pointing to the distinctive features.
She wants to educate other parents expecting twins to question doctors about TTTS.
Dr. Johnson said, "When the doctor says 'congratulations you have twins,' you smile and say 'do I have one placenta or two?' If you have one placenta then you're then you are going to start the path of seeing what's going on. If you have two, oh well, get a bigger house and set aside a college education fund but you are going to be ok in most cases."