Here are two Core exercises that you can do during Pregnancy and Postnatal to help improve Core strength and heal Diastasis Recti.
Seated Leg Lifts: 2-3 x 10-14 Lifts
Exhale and contract just before you lift your leg.
If you can try and do this exercises in front of a mirror so you can watch your hips and torso.
One side is always harder
Try not to grip with the foot that stays on the floor.
Support Extensions: 2-3 x 10-14 lifts
Late Pregnancy and early postnatal stay in close to the ball/sofa.
Keep your pelvic still and control the load.