Muggle-borns and half-bloods. Purebloods can do whatever they like. Which is why, [ she says briskly, ] if at all possible you're not going in Ministry to register. If you do, you're going to tell them you're a Potter and you're not going to mention me at all.

You'll still get the Trace due to being underage, but you'll be marked pureblood. They'll automatically assume a Potter had a child with another pureblood.

[ she shrugs. ] It's the easiest way of things until we can get you home.