About 20 years ago I was thrilled to have Random House publish my parent guide, The Happiest Baby on the Block. In it, I shared my belief that one of the most important things for new parents to understand was a pretty unknown idea called the fourth trimester. Today, that obscure name has so thoroughly penetrated the minds of parents and doctors that the celebrated Merriam-Webster dictionary has included it in their newest edition …and I could not be prouder.