A woman in Israel gave birth to a baby girl who had the embryo of her twin in her abdomen, according to The Times of Israel. The condition, called fetus-in-fetu, is unusual type of parasitic twin, where the one baby develops around another baby and absorbs it into its body.
“It’s just a super rare anomaly,” Dr. Neeraj Desai, managing physician of the maternal fetal medicine division at Orlando Health Winnie Palmer Hospitalin Florida, who did not treat the mother in Israel, told TODAY Parents. “It’s not something that a regular person should even think about worrying about what could happen to their baby.”
Fetus-in-fetu is so uncommon that few doctors would likely encounter it in their careers. An article in Pediatrics estimates they occur in one in 500,000 births. Desai said often the underdeveloped fetuses are found in the abdominal cavity of the surviving baby, and that makes people think that one baby consumed the other. But that's not exactly accurate.
“(As babies develop) we kind of fold in on ourselves so the one twin almost encapsulates the other developing twin and that’s how it gets inside. But then it starts to use the blood supply of the ‘healthy’ twin and so in that regard it’s like a parasitic twin,” he said.
That gives the absorbed twin enough blood to grow organs and bones, but just enough to partially grow.
“It will never develop the full baby because it never gets enough of what it needs,” Desai said. “If this baby inside were to get just as much blood from inside the other baby then potentially it could develop into a whole baby. But it will never be in that big of an environment.”
Doctors once believed fetus-in-fetu was a teratoma, a type of cyst with human tissue in it, such as hair or bones. While some teratomas can be malignant, fetus-in-fetu is normally benign.
“Women get teratomas in their ovaries,” Desai said. “What happens in teratomas these stems cells don’t know what they’re supposed to do and they start growing in the wrong place, and in the end you see like a mix of hair and bone and skin tissue … just a hodgepodge of different tissues in one mess.”
Doctors can normally tell the difference because of how a fetus-in-fetu looks.
“It’s a very specialized development ... you actually see a spine, you see the legs,” he said. “When you see that difference you might say well actually that’s essentially a fetus, or at least a partially developed fetus because — as crazy at it sounds — it looks like a developing baby.”
In the case of the baby born in Israel, doctors first noticed that the girl’s stomach looked bloated during an ultrasound of her mother while still pregnant. After her delivery, doctors examined the newborn and used ultrasounds and X-rays to understand the nature of the mass inside her.
“We were surprised to discover that it was an embryo,” Dr. Omer Globus, director of neonatology at Assuta Medical Center in Ashdod, told "The Times of Israel." “We think that there was more than one there, and we are still checking that.”
Desai said fetus-in-fetu is normally discovered after birth in children under 2, though some have been discovered in adults. Doctors performed surgery on the infant in Israel to remove the growths and they have identified bones and a heart in the two masses they removed, according to "The Times of Israel." Mom and baby are recovering at home.