Surrogate mom delivers two babies, one her own

The lives of Jessica Allen and her husband, Wardell Jasper, were changed permanently and for the better by a rare medical phenomenon. Their unique story begins with the hope of extending a lifeline to another couple around the globe.

Allen, 31, a California mom with two growing boys, decided to become a surrogate mother and carry the baby of another couple, she told the New York Post. Although the $30,000 paycheck (plus expenses) would benefit her family, she also yearned to share the joy she knew by helping a woman who struggled to give birth.

"No woman in the world should have to live their life without experiencing the love and the bond from a mother and a child," she told ABC News.

Working with a San Diego-based surrogacy agency, Omega Family Global, Allen was matched with a couple from China, where the use of surrogates is illegal.

In April 2016, a single male embryo from the couple was implanted in Allen's uterus at an Irvine-based in vitro fertilization center. Nine days later, blood tests confirmed the pregnancy.

Unexpected news arrived six weeks later during her checkup; while examining her, her doctor said, "Well, I definitely see that there is another baby," she told ABC News.

Allen said her doctor explained to her that "the chance of an embryo splitting is very small, but it does happen," and this split meant the second baby was an identical twin of the first. Allen felt surprised but also happy for the Chinese couple.

A bonus was that her payment was increased by $5,000 for the second child.

At 38 weeks' gestation, on December 12, 2016, Allen delivered what she believed to be identical twin boys via cesarean section at Riverside Community Hospital, she told the New York Post. Though she never saw the babies herself, she was shown a photo.

"I did notice one was much lighter than the other -- you know, obviously," she told ABC News. "They were not identical twins."

A month later, there was some shocking news. A DNA test confirmed that the second baby was not a twin to the implanted embryo -- but actually Allen and her husband's biological son.

"I don't know how to describe it. We were floored. We were like, how did this happen?" she told ABC News.

Omega Family Global's lawyer, Matthew Faust, said the agency is unable to address any particular facts of this story.

CNN has not been able to reach the California couple.

An unusual occurrence of superfetation might explain what happened, but one expert believes it may be more complicated than that.

Rare phenomena

"Superfetation is generally defined as becoming pregnant while the mother is already pregnant," David Haig, a professor of biology at Harvard University who was not involved in the surrogacy, wrote in an email. However, he added, "the surrogacy means that it doesn't fit neatly into the classical definition of superfetation."

Superfetation is sometimes suspected when twins, at birth, are very different sizes and so apparently different ages.