Health & Wellness

Pregnant with twins? Ask your doctor this important question

Twin pregnancies are known to come with more risks and challenges — premature birth or low birth weight, for example — but there is a complication that even some doctors may not be aware of: a rare condition affecting identical twins known as Twin-To-Twin Transfusion Syndrome.

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Twin-To-Twin Transfusion Syndrome: Moms join together to raise awareness

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During pregnancy, most identical twins share a single placenta and TTTS develops in 5 to 15 percent of those cases, affecting about 6,000 infants each year. It is rare, but without treatment, it is associated with a 95 percent mortality rate for the babies.

The condition isn't inherited and there's nothing that can prevent it.

“TTTS is not caused by genetics, it’s nothing the mother ate or drank. It's kind of like happenstance, as being struck by lightning,” Dr. Ramen Chmait, neonatal surgeon at University of Southern California, told TODAY.

Read more: Twin-to-Twin Transfusion Syndrome: What one mom wishes she'd known

Early screening and diagnosis are crucial. When a expectant mother learns she is having twins, one of the most important questions for her doctor should be:

“Do I have one placenta or two?”

The placenta is an organ that attaches to the mom's womb and gives the baby oxygenated nutrients. When twins share one placenta, they also share blood vessels. In TTTS, the amount of shared blood becomes unbalanced, with one fetus getting too much and the other not enough.

"Basically, each baby is in jeopardy, but for polar opposite reasons," Chmait said.

"The smaller donor twin is losing blood volume — the baby is basically losing nutrients to the other twin. The other baby gets an excess amount of blood volume."

Doctors say women pregnant with twins should be aware during the first trimester whether they share one placenta. In the second trimester, when TTTS most often develops and can only be detected by ultrasound, women need to be particularly vigilant.

"Sometimes, things can look stone-cold normal and within very few days, it can accelerate,” says Chmait. “It's a very important situation because there's such a high risk of losing the pregnancy. But there is a treatment, so we need to be vigilant.”

Warning signs include:

  • rapid growth of the womb
  • abdominal tightness and cramping.

Read more: 7 Things to Know About Twin-To-Twin Transfusion Syndrome

If an ultrasound determines a woman has twins with a shared placenta, she should get an ultrasound every one to two weeks throughout the pregnancy.

"I didn't know anything could go wrong," said Ode Snyder, who was pregnant with identical twins who shared one placenta. She was diagnosed with TTTS after doctors noticed a size discrepancy between the babies during her 16 week ultrasound.

After Chmait used a laser to seal the shared blood vessels and restore equal blood flow to the twins, Snyder gave birth to Griffin and Zachary.

"I was very lucky: I gave birth to amazing and healthy children," she said.

During pregnancy, the treatment may include repeated amniocentesis or laser ablation to pinpoint the blood vessel connections between the babies, allowing doctors to physically cut them and seal them, Dr. Larry Rand, director of the Fetal Treatment Center at UCSF, explained to NBC News earlier.

After birth, the donor twin may need a blood transfusion to treat anemia, while the recipient twin may need to take medicine to prevent heart failure, according to the National Institutes of Health.

With early detection and the laser ablation, there is a 65 percent chance of having two surviving babies and an 85 percent chance that one of the twins survives, Rand told NBC News.

Resources for moms:

Twin-to-Twin Transfusion Syndrome Foundation — Questions to ask your doctor, warning signs to look for, support groups, resources to assist in planning for delivery and a list of credible neonatal specialists who perform laser ablation surgery to treat TTTS

American Pregnancy Association — Information on TTTS treatment options and a toll-free helpline that provides instant answers and resources

National Institutes of Health — Background on TTTS and resources for expectant moms, including links to medical research and articles

More from NBC:

7 things you need to know about Twin to Twin Transfusion Syndrome

What one mom wishes she’d known about TTTS

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