(NYTIMES) - It was a July morning that began as ordinarily as any other day: Make breakfast. Feed the dogs. Take vitamins. Find that missing sock. Pick up the rogue crayon that rolled under the table. Throw my hair in a ponytail before getting my son from his crib.

After changing his diaper, I felt a sharp cramp. I dropped to the floor with him in my arms, humming a lullaby to keep us both calm, the cheerful tune a stark contrast to my sense that something was not right.