USA Today
Imagine finding out you’re pregnant, but then learning you’re pregnant again just a few weeks later. That’s exactly what happened to one British woman.
Rebecca Roberts, 39, was diagnosed with superfetation, the formation of a fetus while another fetus is already present in the uterus, after the tech at her 12-week ultrasound appointment noticed she was carrying another baby who was less developed, according to the Washington Post.
“We were concerned because the second twin was much smaller. It was only by regularly scanning and seeing that the rate of growth was consistently three weeks behind that we realized it was superfetation,” Roberts’ obstetrician David Walker told the Washington Post.
Dr. Ilina Pluym, an assistant professor of maternal and fetal medicine at the University of California, Los Angeles, said the condition is so rare doctors don’t know the prevalence of the phenomenon.
“There’s only been a handful of reports of it in the world’s literature,” Pluym told USA Today. “It’s more common in fish, rodents and bunnies.”
The condition is scarcely diagnosed because when a woman becomes pregnant her hormones tell her body to not conceive again. Women undergoing fertility treatments are at higher risk, but the chances of it happening are slim.
A 2008 report published in the European Journal of Obstetrics & Gynecology and Reproductive Biology noted less than 10 cases of superfetation had been recorded worldwide at the time.
Not only are the chances of being diagnosed with the condition tremendously rare, but it is also hard to prove, according to Pluym
“We have common answers to why twins can be different sizes,” Pluym said. “The last thing to think on our list is superfetation.”
The more than likely answer for different sized twins in the uterus is one fetus’ placenta not being as healthy as the other one, she said.
If superfetation is suspected, a woman’s pediatrician can check the maturity of the baby once it’s born. Twins can come out different sizes and weights for a multitude of reasons, but doctors can easily tell if one twin was born premature, while the other twin is full-term, according to Pluym.
Pluym once suspected one of her patients may have experienced the rare condition, but it wasn’t the case.
“It’s not supposed to happen in humans, and it’s easy to disprove, hard to prove.”
This news originally appeared on USA Today.
