As Little Things points out, both women wanted to carry the baby, but Bliss did not actually want to give birth. This posed a problem because traditional methods did not offer the ability to do this. That's where the science comes in:
They eventually met with a fertility specialist, Dr. Kathy Doody, who introduced them to a special type of in vitro fertilization called effortless reciprocal IVF.
Instead of using incubators, the eggs and sperm from a donor went into a device that was placed into Bliss’ body. That’s where the eggs were fertilized and the embryos began to develop.
After five days, the device from removed from Bliss and the embryos were frozen. One was then placed into Ashleigh for the full nine months. As US Weekly points out, it became a special moment for both:
“Bliss got to carry him for five days and that was a big part of the fertilization, and then I carried him for nine months,” Ashleigh explained. “So that made it really special for the both of us — that we were both involved. She got to be part of it, and I got to be part of it.”