Diastasis Rectii is a separation of the midline vertical pair of abdominal muscles also known as the Rectus Abdominus muscles. These muscles have a lining know as the rectus fascia which holds them together in the center of the abdomen. When the abdomen gets stretched out, like in pregnancy, the rectus fascia gets loose and is unable to hold the rectus muscle together tightly in the midline. This looseness of the rectus muscle fascia is called diastasis rectii. It is because of diastasis that the tummy of women after pregnancy seems loose, even when the pre-pregnancy weight has been achieved. The diastasis can be corrected with a tummy tuck procedure.