However, Cotter has safely carried and delivered four children: Amelie, 5; Harvey, 3; and 15-month-old twins Maya and Evie.
The mother carried her three daughters in her right womb, while Harvey grew in the left.
"From quite early on, Ben [Cotter's husband] and I discussed having children and it was clear that he really wanted to be a dad," Cotter said.
"I knew I had to be open and honest and tell him that might not be a possibility for me."
"Luckily he wasn't bothered. We talked it through and agreed that there was more than one way to have a baby if you wanted it badly enough."
"But actually, we have found it easy to fall pregnant – I am not sure why, or if it has anything to do with my two vaginas."
While fertility was not an issue for the parents, Cotter was warned by doctors about the possibility of miscarriages and stillbirths as her wombs were so small.
"We decided to give it a go, and just see what happened. We knew it might be a bumpy road and tried not to get our hopes up too much," Cotter said.
"Just a month after we started trying, I bought a stack of pregnancy tests and started taking them weekly.
"Then one morning, I had a test to hand, and there on the stick was a very, very, faint blue line.
"I couldn't be sure, so I took a test each morning that week, and each day the line got darker and darker until I was sure - we were pregnant."
The pregnancy of Amelia in 2014 went problem-free, as did Harvey's 18 months later.
After the birth of two healthy children, Cotter was fitted with a contraceptive implant as she didn't know if she wanted any more children. The implant caused the mother migraines and, months after removing it, she fell pregnant with twins.
"Shocked doesn't begin to cover it. During 17 years together, Ben and I had only ever got pregnant when we'd planned it. Now, here we were, having surprise twins," Cotter said.
The twin girls were delivered by Caesarean in June 2018 and initially seemed perfectly healthy.
A few hours later, Evie struggled to breathe and went into intensive care. An x-ray showed that she was suffering from a congenital diaphragmatic hernia, which occurs when the baby is born with their intestines in the chest cavity.
At five days old, she had keyhole surgery, which the Cotters were informed came with only a 50 per cent survival rate.
The baby girl made a full recovery and is now happy, and healthy.