Miscarriage, or the loss of a pregnancy, is disturbingly common -- so much so, that if you haven't had one, you likely know someone who has. Though it's impossible to say how many pregnancies end in miscarriage, as many occur before a woman knows she's expecting, the Mayo Clinic reports that at least 10% to 20% of pregnancies result in a loss. Still, it can be difficult to know how to comfort those who are grieving.