Most people think of pregnancy as a nine-month, three-trimester event, but more and more professionals consider the 12 weeks immediately after you have your baby as the fourth trimester. The term is new, but every mother and newborn baby will go through it, and it can be a time of great physical and emotional adjustment as both of you adjust to a new life.

What is the fourth trimester?

The fourth trimester, or the 12 week period right after you have your baby, is a period of major growth and development for both parent and baby. Dr. Harvey Karp was the first pediatrician to popularize the idea of the fourth trimester because he thought human babies were born too soon.

The goal of the fourth trimester is to try to think of newborns as fetuses outside the womb for the first three months of their life. During this period, there may be plenty of swaddling and skin-to-skin contact. The bulk of the fourth trimester for your baby will be filled with feeding, sleeping, and crying. Newborn babies eat every 2 to 3 hours or 8 to 12 times per day. They also sleep for over two-thirds of the day. Unfortunately, they sleep between eating, so that means that this new schedule can be quite erratic until they get older.

Parents also experience major changes during the fourth trimester because they are adjusting to a whole new life. Birthparents may be dealing with postpartum pain, breastfeeding challenges, and fluctuating hormones, along with typical newborn sleep deprivation.

While pregnancy is considered three trimesters, pediatricians are beginning to call the first three months of a baby’s new life the fourth trimester. These first three months come with many changes for parents and babies, so even though it is not discussed more often, it is a period all babies and parents will go through.