Pregnancy is one of the most fascinating (and some would argue "beautiful") parts that humans offer, but it can also get really, really weird. In one of those moments that makes you say "how is this real," a woman in California became pregnant while already pregnant. She effectively gave birth to "twins" who were not conceived at the same time and very genetically different from each other.
Jessica Allen was a surrogate mother for a Chinese couple. The soon-to-be parents from China paid Allen $30,000 USD for an IVF treatment and being implanted with an embryo. The embryo took and Allen and the doctors were happy. Allen wanted to use the payment to save for a house. She also told ABC News that she wanted the Chinese couple to experience parenting.
"No woman in the world should have to live their life without experiencing the love and the bond from a mother and a child," Allen told ABC News. At least 10 percent of women in the United States alone struggle with getting pregnant or staying pregnant, according to the Center for Disease Control and Prevention.
During a routine checkup six weeks into the pregnancy, doctors noticed that there wasn't just one fetus -- there were two. Initially, Allen and her husband wrote it off as twins for their surrogates rather than her own child.
"He started moving the ultrasound around and he goes, 'Well I definitely see that there is another baby,'" Allen said. "The chance of an embryo splitting is very small, but it does happen, and I just thought ... I was very surprised."
Allen said she believed she was delivering twins until the moment she saw them out of the womb. She was never given the chance to see the babies in person but knew there was a difference.
"I did notice that one was much lighter than the other," Allen said. "You know, obviously they were not identical twins."
This nagging sensation that something wasn't quite right sent Allen and her husband on a quest to figure out why. Months later, she discovered that the second baby wasn't a twin at all but her own biological child. This sparked a 10-month battle to get her son back in her life.
Allen's husband Wardell Jasper also noted, "You got to think like, 'Wow, we didn't know you were coming... We didn't plan this."
How did this happen?
The general rule of thumb for pregnancy is that you can't get pregnant again after you're already pregnant. However, what happened to Allen is something that rarely occurs in the mammal world. Superfetation is when two offspring develop inside a mother at different stages of development.
It sounds incredibly high risk, but the researchers say it's actually not much more dangerous than any precautions a mother might take having a normal set of twins. The biggest risk is that the second child is delivered prematurely before the lungs can fully develop.
Other mammals have exhibited this behavior before, including rats, horses, kangaroos, and even other primates. While it's been documented in a wide variety of studies, the precise conditions for superfetation aren't pinpointed yet.