Heavily pregnant with a second child, Heather Lanier deliberately read a book by a mother whose infant son was dying. She’s not a masochist, only a realist. “I needed this story,” Lanier writes.

In Psalms of Unknowing, Heather Lanier finds eloquence and profundity from such unlikely sources as a GBS test, a culture done between 36 and 38 weeks of pregnancy that involves a sample from the ...