A healthy baby girl weighing 9 pounds was born with two fetuses inside her, according to a study just published in the Hong Kong Medical Journal. The extremely rare occurrence, called fetus-in-fetu, happens in just one out of every half million births. The little girl, born in 2010, recovered from the operation to remove the fetuses.
In fact, there’s not even total agreement that the conjoined tissue masses should even be called fetuses. Some doctors favor the term teratoma, which is a mature type of tumor, over fetus. Yet the two forms had spines and “ambiguous external genitalia” though they had not yet developed skulls.