TAPS Awareness Day: The spontaneous blood cell imbalance that can be sudden and deadly in monochorionic twins

At 31 weeks and 5 days pregnant with identical twins, Amberlyn Smith went to her bi-weekly ultrasound feeling confident. Just two weeks prior, both of the twins had grown appropriately and screening tests came back normal. But that day, Dec. 23, there was a clear discrepancy in their size, as well as a notable abnormality in their blood flow. Smith was immediately sent to see an intervention specialist with The University of Texas Health Science Center at Houston (UTHealth) at Children’s Memorial Hermann Hospital, where she emergently delivered the twins the next morning, on Christmas Eve.

Smith was diagnosed with twin anemia polycythemia sequence (TAPS), a condition in which twins develop unequal blood counts, where one does not receive adequate blood flow and is notably small and anemic and the other twin is overloaded with blood and notably swollen, or plethoric.  According to Ramesha Papanna, MD, MPH, a maternal-fetal intervention specialist with McGovern Medical School at UTHealth, TAPS occurs in about 5-10% of pregnancies with identical twins that share a placenta but not an amniotic sac, known as a monochorionic diamniotic twin pregnancy.

“Learning about TAPS was like reading the back of a medicine bottle when you realize all these horrible sounding side effects could happen and your mind is just spinning,” Smith said.

Smith met Papanna at the hospital, who did additional screenings and told her she needed to stay in the hospital for monitoring. He said sometimes the blood imbalance can stabilize, but it could also get worse very quickly, which is what happened in Smith’s case.

“At that point, I knew the babies were sick, but not very sick,” said Papanna, who is affiliated with UT Physicians, the clinical practice of McGovern Medical School, and The Fetal Center at Children’s Memorial Hermann. “When I re-evaluated her the next morning, things had progressed quickly and the recipient baby’s heart was failing, so we made the decision to proceed with delivery.”

 “It was shocking, but I’m just so thankful they caught it when they did,” Smith said. “Not all parents of babies with TAPS are so lucky. Dr. Papanna was so calming and had such a professional bedside manner the whole time – he really put me at ease.”

After the babies, Steven and Hudson, were delivered, they spent some time in the neonatal intensive care unit, and are now home and doing well.

In TAPS, one baby has blood that doesn’t have enough red blood cells, making it too thin, like water.  The other twin’s blood has too many red blood cells and is too thick, like ketchup. The twin with watery blood is referred to as anemic and the twin with ketchup blood is called polycythemic. The polycythemic twin’s blood can be too thick to reach its brain and limbs, so the anemic twin tries to transfuse its blood through a few small blood vessel connections, but this can cause too much blood loss from the anemic twin, as well as blockage in the polycythemic twin. Papanna said the anemic baby is most at risk of dying, which happens in about 10% of cases.

This change in blood flow can happen spontaneously in monochorionic twin pregnancies, which is why Papanna said it was critical that Alexandria Hill, MD, the maternal-fetal medicine specialist who initially saw Amberlyn, immediately referred her to Papanna for potential fetal intervention.

To detect TAPS, sonographers use Doppler technology to detect the blood flow levels in the middle cerebral artery (MCA). Smith’s ultrasound revealed that the smaller twin’s blood was flowing at twice the normal rate, while the other was flowing at half the normal rate.

“Amberlyn’s sonographer, Kaylee Weston, did a great job detecting the elevated blood flow levels in MCA of the smaller twin, which is what helps us to identify fetal anemia,” Hill said. “Measuring a fetal middle cerebral artery can be difficult. If you catch it even slightly at the wrong angle, the numbers can be off. The interesting thing about Amberlyn’s case was that although the twins were sharing one placenta, you could see a clear demarcation of what portion of the placenta was being used by the anemic twin versus the plethoric twin. When I called Dr. Papanna, we discussed this as a concerning ultrasonographic finding of progressing TAPS.”

Joey England, MD, a maternal-fetal medicine specialist with Maternal-Fetal Consultants of Houston, who was also heavily involved in Smith’s care, highlighted the importance of women with twin pregnancies making sure they start seeing a maternal-fetal medicine physician early in their gestation, preferably before 16 weeks, so that the type of twins can be diagnosed. She said referring quickly to a maternal-fetal interventionalist practice, such as The Fetal Center, is important for cases such as TAPS where immediate fetal surgery may be required.

For other women to have the positive outcome that Smith did, physicians say the standardization of screening protocols is key moving forward. Hill noted that the routine evaluation of MCA blood flow in monochorionic twins is viewed as “discretionary” and not a requirement in standard protocol management.

“Nothing in the current recommendations say that MCA evaluations are required every two weeks starting around 16 weeks for monochorionic diamniotic twins, but most maternal-fetal medicine specialists will perform these evaluations to screen for TAPS. The problem we often face is that twin pregnancies are not referred to us until the third trimester or when their primary provider sees something unusual, and sometimes that is too late to catch things like TAPS or twin-to-twin transfusion syndrome (TTTS),” Hill said. TTTS is a condition that is similar to TAPS, but more well-known and more routinely screened for than TAPS. In TTTS, there is a notable difference in the amniotic fluid volume between monochorionic diamniotic twins.

“If they didn’t screen her for MCA and caught the imbalance when they did, those babies would not have made it,” Papanna said. “Screening for TAPS is critical, even though it’s a rare condition and we, as physicians, are still learning about the disease. If we don’t catch it early, we don’t even get the chance to treat it, since it progresses so quickly.”

Papanna noted that anyone who learns they are pregnant with twins should make sure they know if the twins share a placenta, and what kind of twins they are having.

 “Women need to know if their physicians are tracking their MCA values and if they’re knowledgeable about TAPS, not just TTTS,” Smith said. “I remember after my ultrasounds, people asking, ‘What is the gender. Does the baby have hair?’ without realizing that because I was having monochorionic diamniotic twins, my doctor was scanning for lifesaving values like blood flow to the brain. I didn’t care about that aesthetic kind of stuff, but I understood why they didn’t grasp the situation since so few people know about TAPS.”

The Fetal Center is a national referral center and international leader in fetal diagnosis, intervention, and comprehensive care for many fetal diseases like TAPS.

“We’ve seen well over 30 patients in the last five years and case numbers are going up, due to increased screening. These cases, as well as our collaborations with other specialists across the world, have helped us start to understand differences between TAPS and TTTS, and the best way to treat it,” Papanna said.

Papanna is also leading and contributing to research at UTHealth that is focused on the best way to screen for TAPS, the effects TAPS has on the pregnancy, and the best way to treat TAPS patients.

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