Beyonce gave birth 2 weeks ago Tuesday, but she and Jay-Z are still dealing with premature birth issues ... sources connected to the family tell TMZ.

Sources familiar with the situation tell us, as of 4 days ago the infants were still in the hospital. As we reported, they are "under the lights" ... which typically means they have jaundice, the result of elevated bilirubin issues. The lights lower bilirubin in the blood to eliminate the jaundice.

We're told none of the medical problems should pose serious long-term issues ... nonetheless, we're told doctors did not want the babies released until they were stabilized.

As we reported ... Beyonce had a boy and a girl.

The release date is unclear.