It is not safe to wear them just after giving birth. I wouldn't recommend it from a medical perspective... A midwife needs to check that a woman's uterus is going down after birth. Wearing that could hide the fact that a woman's uterus isn't going down, and conceal internal bleeding.
While medical professionals are concerned about their use, it's hard for some women to deny themselves a quick fix. So tell mommy, are you a fan of belly binding garments?