Your baby's first ~3 months is basically the "4th trimester" but just outside the womb. It basically explains why things like swaddling work so well for their sleep at this age, and why shush sounds work (because it supposedly mimics how the baby hears the mother breathing inside the womb of the mother). Also counter-intuitively to a new parent, why perfect stillness didn't really matter for her sleep and actually a little movement ended up being better. Invest in a good rocking chair is probably the best advice I can give any parent! Don't cheap out here, you are going to be spending a lot of time in it!
