Over the weekend, reports surfaced about a “minor issue” with the birth of Beyoncé and JAY-Z’s twins. Now, TMZ reports that the issue deals with post-natal complications due to premature birth.

According to the report, Beyoncé did not go full-term with the pregnancy and she has been at the hospital since their birth on Monday (June 12).

Insiders say that the babies are “under the lights,” which TMZ notes is a term that is used when babies have jaundice or icterus due to high bilirubin levels in the blood.

MedLinePlus defines bilirubin as “a yellow substance that the body creates when it replaces old red blood cells.” High levels of this can sometimes make the baby’s skin and eyes appear yellow.

Jaundice is more likely to occur with premature babies. MedLinePlus notes that “special blue lights” are sometimes used on infants with “very high” levels in a treatment called phototherapy. This is not deemed to be particularly dangerous.

JAY-Z and Beyoncé have not issued an official public statement about their new children yet. However, Queen Bey’s father Mathew Knowles celebrated their arrival on social media.

The babies’ genders have not been revealed yet, however TMZ has reported that they are a boy and a girl. The Carter twins add to JAY-Z and Beyoncé’s growing family, joining their big sister, 5-year-old Blue Ivy.