We call the first three months of a baby’s life the fourth trimester because they often act like they want to be back in the womb, but it’s also the fourth trimester for the mom. Her body is experiencing many of the same physiological realities of pregnancy (the hormone relaxin, stretched out abdominals, back pain) AND also trying to recover from childbirth. For moms the fourth trimester is a massive physical challenge, on top of also being a sleep deprived, hormone-fueled emotional roller coaster.