Fourth trimester
Also called 4th trimester, the fourth trimester
The fourth trimester is the first 12 weeks or so after a baby is born, a time of adjustment for the baby and recovery for the parent. The name treats those weeks as one more stage of pregnancy.
How it's said
We've accepted it's the fourth trimester and that he just needs to be held...
Coming to the end of the fourth trimester. Now what?
I know to you it feels like she's been here for an eternity, but really she is still properly in the 4th trimester.
Who says it
Where it came from
US pediatrician Harvey Karp coined the label in his book The Happiest Baby on the Block. It rests on an older idea, sometimes called physiological prematurity, that human babies are born less developed than other primates.
The phrase has since moved into medicine. In 2018 the American College of Obstetricians and Gynecologists revised its postpartum care guidance to stress the importance of the fourth trimester, and hospitals now name postpartum services after it.