here's the blog post he made about it

Some many years ago, long before I started the comic, I was in a relationship and we suffered a miscarriage. Now, this relationship was toxic to begin with and doomed to fail regardless, so that the miscarriage was the straw that broke the camel's back came as no surprise. It was a pregnancy neither of us wanted in the first place, so the event didn't effect me nearly as much as it would, say, a couple who was trying for a child. Still, I saw the emotions it can bring up first hand, and I saw how it could truly hurt someone. It's a tough thing to handle because it's nobody's fault. There's nobody you can blame.