Rare twin pregnancy requires careful medical care from diagnosis through delivery

Carrie Zirbes, mother of three, had seen her share of ultrasound images. She knew right away that something was different about the ultrasound to confirm her fourth pregnancy. 

There was the usual fluttering of the heartbeat, but also an odd blob. As Carrie and her midwife looked closer at the baby, they got a wave. 

“All of a sudden out of the background comes this wiggling hand,” Carrie said. “So we had a baby in the front and then a wiggling hand in the back." 

The wiggling hand belonged to a second baby. Carrie was pregnant with a rare form of twins. 

“Monochorionic-monoamniotic twins are monozygotic, meaning one embryo splits after the placenta and amniotic sac have already formed. There is only one placenta, one amniotic sac, but two babies,” explained Yasuko Yamamura, MD, a maternal-fetal medicine doctor with M Health Fairview and an associate professor at the University of Minnesota Medical School. 

Unlike typical twins, which have their own placenta and amniotic sac during pregnancy, monochorionic-monoamniotic, or mono-mono, twins share just one of each. With the exception of conjoined twins, this is rarest and highest-risk type of twin pregnancy.  Mono-mono twins are at a high risk of cord entanglement, heart defects, and twin-to-twin transfusion syndrome, which is when one twin gets more nutrients than the other. Doctors closely monitor mono-mono twins.  

“Specialized care and close monitoring are important for monochorionic twins,” Yamamura said. “Our goal is to watch the babies very carefully throughout the pregnancy so we can respond quickly to any concerns and give both babies the best chance to stay healthy and safe." 

Specialists in maternal-fetal medicine, neonatology, genetics, and pediatric cardiology as part of the M Health Fairview Maternal-Fetal Medicine program, met regularly to review Carrie’s fetal monitoring data and adjust her care plan as the pregnancy evolved. 

The care team also carefully planned to deliver the babies at M Health Fairview Masonic Children’s Hospital, where a Level IV neonatal intensive care unit was prepared for premature babies with heart and respiratory complications. 

Prepared for complications 

Careful monitoring allows clinicians to respond immediately to sudden changes in fetal movement or blood flow that can become life-threatening. And they did when the babies experienced twin-to-twin transfusion syndrome. 

“Baby B, who is now Phoebe, was sending all of her blood and everything through the placenta to baby A, Fiona,” Carrie explained. 

Phoebe was severely fetal growth restricted and anemic. Meanwhile, Fiona had cardiomyopathy. Her heart was failing because she was overwhelmed with more fluid than her kidneys could handle.  

The twins needed a placental ablation, a rare procedure to cut the vessels connecting the two. The procedure would give them the best chance to survive, but it also comes with a high risk of losing one or both babies. 

The procedure was successful. Carrie checked into the hospital at 25 weeks, so the babies could continue growing and developing. After 6 weeks in the hospital, at 30 weeks and two days, Carrie’s monitors revealed that contractions were starting.  

On May 29, 2025, Fiona was born first and had to be resuscitated. She also has a right aortic arch, which is when the large blood vessel bends to the right around the trachea instead of to the left. It made breast and tube feeding difficult. The babies spent June and July in the NICU, where Carrie visited them every day. 

Fiona went home August 21 with a feeding tube, but continued to have feeding issues. Doctors thought Fiona would need open-heart surgery to relocate her aortic vessel, but the fix ended up being much easier – just a quick snip of the vessel was enough to reposition it. Carrie called it “an absolute miracle.” 

One year later 

Now as they look forward to their first birthday, Fiona and Phoebe have finished physical therapy. They are small, wearing three-month-sized clothes, but have no developmental issues. They’re doing everything they should be and are active, happy, and beautiful, Carrie said. But she can’t help but remember those uncertain months. 

“We kept hearing their survival rate for mono-mono twins is about 70%," she said. "Then lower with twin-to-twin transfusion syndrome. There aren’t even numbers for all the variables they experienced. It’s just rare, and they're doing great now.”