Rare ‘Mono Mono’ Twins Defy Odds and Thrive
August 3, 2026
The Zirbes family was in for a surprise when Carrie Zirbes and her husband found out twins were on the way. Already parents to three children, they were astounded to learn the twins were not just identical, but a rare type known as monoamniotic or “mono mono” twins.
Identical twins are common in about 1 in every 250 pregnancies, but mono mono twins are significantly rarer, occurring in only about 1 in 10,000 pregnancies. These twins share both a single placenta and amniotic sac, which poses significant risks due to the potential for their umbilical cords to entangle, threatening the babies’ oxygen and blood supply.
Upon hearing the news, Carrie expressed, “I think I’m still trying to wrap my head around how rare it is, actually.”
Given the high-risk nature of the pregnancy, Carrie was admitted for hospital bed rest to allow doctors to monitor the twins closely. As the pregnancy continued, complications arose when one of the twins began transfusing blood to the other, causing Baby A to be smaller and have an enlarged heart.
At 30 weeks, the medical team decided it was time to deliver the twins. The delivery was tense, especially when Fiona, initially referred to as Baby A, was born not breathing and required intubation. Both Fiona and her sister Phoebe were taken to the neonatal intensive care unit, where they received critical care.
After a period filled with uncertainty, the family received good news: Fiona and Phoebe were healthy enough to be discharged and join their family at home.
Now, a year later, Fiona and Phoebe have reached a significant milestone by celebrating their first birthday as thriving, healthy children.
Their journey from a rare and precarious start to a joyous and thriving existence serves as a heartening tale of hope and resilience.
Credit: Carrie Zirbes / Facebook
Credit: Carrie Zirbes / Facebook
