'Julia had planned to leave the hospital on December 3 but she could not leave knowing her baby girl was still so ill.'
The twins were born by caesarean section on November 28. Miss Roberts, 37, is said to be breastfeeding both.
She is thought to have had IVF treatment to help her conceive after trying to start a family since marrying Moder, her second husband, two-andahalf years ago.
She once said: 'I can't wait for kids. I can't wait to hold a baby in my arms.'
Doctors became concerned at the end of October when she started having contractions ten weeks before the due date.
She has remained in hospital ever since. However, she gave interviews from her bed to promote her latest movie, Ocean's Twelve, which also stars George Clooney and Brad Pitt.