An extremely rare condition
The second option, of superfetation, is extremely rare, but not impossible. It can happen only if the couple has intercourse when the woman is already pregnant, but Jessica assured them they did not have unprotected intercourse. The doctors believed it was a case of superfetation, and that somehow Jessica conceived another child during her pregnancy with the Lius’ baby.
A reproductive medicine specialist told ABC news that cases of superfetation were so rare, there were only about 10 pregnancies of this kind reported in medical literature. It describes a simultaneous occurrence of more than one offspring in the same body.