What It Is & Why It Happens
The "recti" is referring to the rectus abdominis which are the long, flat muscles at the front of the abdomen. Basically, these are the "six pack" muscles. Diastatsis recti is when these rectus muscles spread apart due to the added pressure!
Everyone experiences some type of widening, which makes sense when you think about it; however, diastasis recti is when the separation is 2 finger-widths apart or more! You can test this by laying flat on your back, feet flat on the floor, and bending your knees. Gently lift your head from the ground and feel just below the belly button. If it's 2 finger-widths apart or more then you'll definitely want to bring it up to your doctor and have them check it out!
With diastisis recti, the connective tissue becomes weaker and thinner which increases the load on the body and can cause lower back pain. It can also result in that "pooch" a lot of women complain of post-pregnancy because of that space where the ab muscles once met.
How To Treat It
First and foremost, you'll want to avoid any exercises that make the separation worse. These include any frontal exercises (planks and push ups), twisting exercises (ab bicycles, russian twists, etc) and crunches. You'll also want to avoid ab exercises that require both legs to be off the ground (leg lifts, V sits, etc). These put even more pressure on the rectu abdominis which can further the thinning of the connective tissue between the abs. These are also the exercises you'll want to stop doing in the 2nd and 3rd trimester to prevent diastasis recti from occuring!
The exercises you'll want to do are the ones targeting the transverse abdominis. These are the "inner abs" and they act like a corset, keeping everything nice and tight. This muscle, is especially important during pregnancy because it keeps everything "together", keeps the core strong throughout the 9 months, and helps during labour! Working transverse abdominis helps prevent diastasis recti, and also helps treat it (and any type of ab separation that may occur during pregnancy).
Although you won't feel the same "burn" that you do from working your rectus abdominis, it's SO beneficial! You'll be able to get back to regular ab exercises much faster if you don't work the rectus muscles during the 2nd and 3rd trimester.
Here are some good workouts that are safe and effective. I also created a hashtag on my Instagram with good exercises to do #gfspregnancy.