The human body can seem like a total mystery as very few of us actually understand our inner workings. One especially common misconception is that it’s impossible to get pregnant while already pregnant. A rare phenomenon known as superfetation is basically just that.
The New York Times addressed the topic in a recent column after a curious reader asked if two fetuses can development at different stages at the same time.
As previously reported, an Australian couple made headlines last year when the mom gave birth to twin girls conceived 10 days apart. The condition is rare, and a French report from 2008 notes there were fewer than 10 documented cases at the time.
"Pregnancy hormones usually shut down a woman's system, making it impossible for her to ovulate during her pregnancy," Connie Hedmark, an obstetrician at Marquette General Hospital in Michigan, explains to BabyCenter.com. "This is why superfetation is so remarkable."
The occurrence is so outside the biological norm that some doctors don’t even believe it’s real.
"Most doctors believe alleged reports [of superfetation] are primarily due to markedly unequal growth and development of twin fetuses of the same gestational age," says Jason James, M.D. and medical director at FemCare Ob-GYN in Miami in an article on Self.com.
Doctors aren’t sure why this happens, but one theory is that a typical hormone spike is suppressed if the first embryo’s implantation is delayed.
Experts also look to fertility treatments as a possible explanation for this rare event. According to PregnancyCorner.com, the second fetus can be conceived up to weeks after the first. However, babies usually are born the same day as doctors either induce labor or deliver via C-section. The website reports that superfetation might be more common than we realize as some doctors might mistake it for twin pregnancies.