Throughout the 36 weeks that Carolyn carried "Little Man," the two couples maintained a respectful relationship. The Morells described in their 2010 book, "Misconception," their own harrowing wait, knowing that with Carolyn's past history of miscarriages, their child might never be born.
In an interview with ABCNews.com, the Savages said that even though they considered it a "gift" to return Logan to his biological parents, the medical mistake tore their lives apart.
Their marriage was under tremendous strain, and after the delivery, Carolyn was diagnosed with post-traumatic stress disorder. Both have sought counseling.
They were in an unusual position: Their son had not died, but he was gone.
"It's a loss that has no closure," said Pauline Boss, professor emeritus at the University of Minnesota, who described the ambiguity in her book, "Ambiguous Loss."
"People have a difficult time resolving this," she told ABCNews.com. "There are no rituals or sympathy cards for them."
"He'll always be my baby, even though he's their son," said Carolyn. "There was no way of entering into a pregnancy and taking a 12-cell embryo and turning it into a human being and not feel a maternal connection to him."
The embryo mix-up happened at a fertility clinic that a legal settlement prohibits the Savages from naming, but the May 2010 agreement required them to explain in writing what went wrong.
A lab employee where the frozen embryos were stored had labeled Carolyn's birth year as 3/19/1967, rather than 3/19/1969 -- a detail that helped identify the eventual error.
Embryos are stored alphabetically, and when the clinic opened the "S" file, it mistakenly pulled an information sheet for Shannon Savage -- now Shannon Savage Morell, who used her birth name at the time of the original IVF procedure.
From that point on, the Morells' embryos were labeled and associated with the Savage's paperwork, and their sheet was tucked in the back of the file.
Oddly, on the day of the transfer, Carolyn had noticed the wrong birth date when the nurse attached her wrist bracelet.
"It had my name, Sean's name, my Social Security and Sean's and my date of birth," she said. "I said, 'Wait a minute, that's not my birthday,' and made a joke. 'I'm not 40 yet.'"
The nurse took a ballpoint pen and changed the 7 to a 9.
Nine days later, a data-entry person filing the paperwork wondered about the conflicting birth year and rifled through the file, finding the Morells' embryo information sheet in the back.
Until then -- five days after the implantation of the embryo -- no one, not even a doctor, had cross-checked the labels and information sheets.
In the first few weeks after learning of the mistakenly implanted embryo, the Savages didn't tell anyone except their lawyer, their priest and a counselor.
"We made the choices quickly," said Sean. "We also knew that we were embarking on a very different journey, but we didn't stop going in that direction, because we thought it was right. But we didn't have a full understanding of what the pitfalls were."
Their story came not long after the shutdown of an in vitro fertilization center at Ochsner Hospital in Elmwood, La., triggered by a possible mix-up in the labeling of frozen embryos. Similar mistakes have been made in clinics in New York and Great Britain.