These Ultra Rare 'Mono Mono' Twins Beat Incredible Odds and Are Now Thriving

August 3, 2026

When Carrie Zirbes and her husband learned they were expecting twins, they were already parents to three children.

The surprise quickly turned into shock when doctors revealed they weren't just having identical twins. They were expecting an extraordinarily rare set of monoamniotic, or "mono mono," twins.

Credit: Carrie Zirbes / Facebook

While identical twins occur in about 1 in every 250 pregnancies, mono mono twins are far less common, occurring in only about 1 in 10,000 pregnancies.

Unlike most twins, mono mono twins share both a single placenta and a single amniotic sac. That creates serious risks because their umbilical cords can become tangled, potentially cutting off the babies' oxygen and blood supply.

"I think I'm still trying to wrap my head around how rare it is, actually," Carrie said.

Because of the high risk, Carrie was placed on hospital bed rest so doctors could closely monitor the babies. As the pregnancy progressed, the situation became even more concerning. One baby was transfusing blood to the other, leaving Baby A especially small with an enlarged heart.

When the twins reached 30 weeks, doctors decided it was time to deliver them.

The first moments were frightening. Fiona, known as Baby A during the pregnancy, wasn't breathing after birth and had to be intubated. Both girls spent time in the neonatal intensive care unit while doctors and nurses cared for them.

After weeks of uncertainty, the family finally received the news they had been hoping for. Fiona (Fion-A) and her sister Phoebe (Phoe-B) were healthy enough to go home.

Credit: Carrie Zirbes / Facebook

Now, one year later, the remarkable twins have reached another milestone.

Fiona and Phoebe recently celebrated their first birthday and are happy, healthy, and thriving.

After a pregnancy filled with uncertainty and months of anxious waiting, their story is now a joyful reminder that sometimes the rarest beginnings can lead to the happiest endings.