Answer: Way to "parent up," Dad.
The better time to talk to him about this, in depth, was before you got pregnant again. I realize how unhelpful this sounds, but I mention it because you might want to open your conversation with your husband by noting that you shouldn't have let his ignorance request go unchallenged.
It's not "the selfish part of you" that's telling you you're in this together. You ARE in this together, co-parents, a team in biological, emotional, financial, and logistical senses. It's not right, fair, or mature of him to delegate unilaterally a huge chunk of the emotional hard work to you.
While a miscarriage is a painful loss, it's not as if carrying a pregnancy into the second trimester will erase all possibility of any other pain. I mean, duh — as a parent, he's going to have to deal with all kinds of fear, pain, and suspense. And since he'll have to suck it up at some point, he might as well start now.
You can have this whole conversation before telling him you're pregnant, but unless he's willing himself into cluelessness he's probably going to guess. For what it's worth — while it will (rightly) feel false to withhold your news, opening with it introduces the risk that your husband will be too focused on the bean-spilling to listen carefully to the why. So, consider leading with the why and getting quickly to the what.
And if he fights you on the idea of emotional accountability and/or gets angry at you for telling, then it's time for a professional referee — either marriage counseling or a marital workshop. You really, really don't want to go into parenthood with someone who thinks it's OK to use the emotional coping tactics of a 7-year-old.
E-mail Carolyn Hax at email@example.com, or chat with her online at noon Fridays at www.washingtonpost.com.