Disclaimer: I am recounting as best I can some of what is in the book, but I am not a personal trainer and I am in no way knowledgeable of what I write! Lol! Read the book! It's good.
How to tell if you have a mummy tummy (diastasis):
You may have bad posture (tend to slouch). And you probably have back/abdominal pain when trying to do things like lift your baby. Your tummy will pooch out too. But to see if you actually have a diastasis instead of a regular flabby tummy, do this check. Lie on the floor on your back with your knees bent. Place your hand flat on your belly, fingers pointing towards your toes. Fingers should be flat on your belly. Check in three places-- belly button, three inches above bellybutton, and also below. To check you press your fingers down as you lift your head. Shoulders stay down. If you feel a gully that you can press at least one finger into then that is a diastasis. The wider the gully, the worse the diastasis. A diastasis can be caused by pregnancy/childbirth, but also by doing too many recti-strengthening exercises without also strengthening the transverse muscles that hold your abdominals together. (The pictures in the book make it easy to understand.)
What NOT to do if you have a Mummy Tummy (diastasis):
Basically, don't do pilates unless you have specialized gym equipment and know what you're doing. Most of the pilates exercises will not only not help your mummy tummy, they will make it worse, or even create a diastasis where tere was none before. Dont do: the 100, crunches, sit-ups, crossover situps, or any other back-lying exercises. When your diastasis starts to heal, you can do certain back-lying exercises only while wearing a splint, but it's not necessary.
Other things that can make a diastasis worse: slouching, bending at the waist to pick up things like your baby or toys, wearing baby in front carrier or sling (better to do this while wearing a splint, or wear baby on back or very high so you're not slouching as you do it), don't suck your lower tummy in while letting your upper abdomen hang out.
What TO do:
Do belly breathing. When you breathe, feel your lower belly expand, and when you exhale, let your lower tummy come all the way back. Do not forcefully puch your upper abdomen out while doing belly breathing.
Practice perfect posture as much as possible. Squat or bend at the knees to lift things or babies.
Carry your baby on your hip or back and try to maintain good paosture when you do (this is one of the hardest things for me.)
When breastfeeding, don't slouch to get breast to baby. Prop baby higher with pillows, or lie down next to baby to nurse.
Do
belly dancing exercises. Stand with your knees bent, legs apart at hip distance, and your hands resting on your thighs so you're bent over a little but your back is nice and straight. Now pull your pubic bone towards your belly button to stretch your lower back. Hold for a count of five, the release to a flat back position. Do 10 tilts at a time, at least once a day.
Do
abdominal work:
Seated Tupler Technique: If you are holding your baby properly, you can do this one while breastfeeding. Remember, pillow(s) under baby, bring him/her up to you, rather than bringing your breast down to them-- no bending! You need to be sitting for this exercise. Crosslegged with back against a wall, or in a chair where your thighs and buttocks are totally supported. The seat should be firm but comfortable. Sit with your butt touching the back of the chair. There are two parts to the Tupler Technique: Elevators, and Contractions. If you are breastfeeding, she suggests switching exercises halfway through when you switch breasts.
Part one, Elevators: sit as described. Place your hands on your tummy, one above the belly button, one below. Take a belly breath and expand tummy to floor one. (Floor 1 is all the way out, floor 5 feels like your tummy is touching your spine, floor six you try to push your tummy outside your back or something.

) Then bring your bellybutton back toward your spine-- floor 5. Imagine your ribs coming together. Hold for 30 counts but count outloud so you know you're still breathing. Then pull your tummy back even further to 6 for a little squeeze, and count as you do 5 of these squeezes, and release. Do a full, deep belly breath. Whew. Do ten sets of these every day.
Part two, Contractions: sit as above. Place hands in the same position, above and below bellybutton. This is so you can feel that both top and bottom are moving backward.
still working on it . . .