"We're excited and terrified and feel so very lucky," the couple said in a prepared statement.
The Savages have been working with a surrogate, Jennifer, to conceive since the birth of Logan in 2009. The little boy, now 19 months old, is the biological son of Shannon and Paul Morell.
Both couples have written books about their harrowing experience after an unnamed fertility clinic confused their records and implanted the Morells' embryo in Carolyn Savage's uterus. She carried the fetus for nine months, then handed the child over to his biological parents.
"When we brought Logan into this world, we came to understand his life was a gift," the Savages wrote. "We are humbled again as one very special woman is giving this same gift of family to us. Jennifer, our carrier -- our partner and guardian angel -- has become part of our family. We are in awe of her generosity and our gratitude is beyond measure."
The Savages had tried for another child through surrogacy last year, but Jennifer miscarried. She is now 19 weeks pregnant with twins. The Savages said they did not know the sex of the babies.
"We've been so humbled by every good wish and blessings we've received from real friends like you," they wrote. "When shock and heartbreak came, you comforted. When we started to lose hope about expanding our family, you squeezed our hands in support and told us to not lose faith."
The couple tells their heartbreaking story in their 2011 book, "Inconceivable."
Just four days after finding out she was pregnant, Carolyn Savage went from the high of expecting the child she had tried so hard to conceive, to the unfathomable low of knowing the baby was not hers to keep.
Carolyn Savage had had a history of miscarriages, and she and Sean turned to in vitro fertilization. They already had three other children and hoped for a fourth.
But On Feb. 16, 2009, the Sylvania, Ohio, couple learned that the frozen embryo of another couple had been mistakenly transferred into Carolyn's womb.
The Savages could have fought for custody, or Carolyn could have had an abortion. Tethered to a strong Catholic faith, Carolyn chose to carry the baby she and Sean called "Little Man" to term.
On Sept. 24, 2009, the Savages returned their newborn son, whom they'd held for 30 minutes, to his biological parents -- Shannon and Paul Morell of Sterling Heights, Mich., who named him Logan.
In the months since Logan's birth, the Savages have had a long, painful, somewhat "ambiguous" journey.
"We have three children. Or do we have four? A strange question, but the kind that parents who have lost a child ask themselves from time to time. That absent child is always with you, a loss you feel some days as yearning and other days in a gasp of pain.
"This was a child whom I nurtured and we both protected from the forces conspiring against his survival," writes Carolyn, now 41, in the book's prologue. "Yet I understand that I may never hold him in my arms again and that the next time I see him, he will think of me as a stranger."