A Minnesota mother has suffered a great loss after delivering a set of conjoined twins this week in a Colorado hospital. According to a report from ABC, Amber McCullough gave birth to daughters Hannah and Olivia, but just one of the twins survived the agonizing separation surgery.

Olivia was not expected to survive the operation, and doctors gave McCullough a fair warning before the procedure began. McCullough remained positive throughout the ordeal, saying that she had faith in her religion and the talent of the doctors at the hospital.

McCullough updated her Facebook friends with posts revealing the latest developments in her pregnancy. She knew that the surgery to separate the two twins, who were conjoined at the abdomen, would be tough on the surviving sister Hannah, but she was calm in her acceptance of the reality of the situation.

“I am determined not only to do all we can to keep her alive but also to ensure she is happy and as comfortable as possible,” McCullough posted. “That being said, naturally there will be some uncomfortable parts of this journey in which case we will also lean on the doctors to manage her pain.”

Conjoined twins are extremely rare, and only happen in one out of roughly 60,000 births. Despite the tragic loss, McCullough is focused on moving forward and making sure that Hannah has the best life possible.