The fourth trimester: Transitioning to life outside the womb

Have you ever wondered why is it that most mammals are born landing on their feet and ready to start walking alongside their mothers just a few hours after birth, but human babies come into the world still unprepared for life outside the mother’s womb? The answer to this paradox lies in the highly complex brain that characterizes our species. A more independent human baby would require more time to further develop the nervous system and the resulting large head-size would make delivery impossible. Although human babies are born full term after 37 weeks of gestation, they are nonetheless developmentally premature and depend on their caregivers for survival. That’s why, for practical reasons, evolution relied on our social nature to help the baby thrive.

Reflecting on these implications, UCLA professor of pediatrics Dr. Harvey Karp proposed the term “fourth trimester” as a way of describing the period of rapid growth and adjustment you and your baby go through after childbirth. From the moment they arrive, babies start soaking up new information, interacting through trial and error, practicing new behaviors, and connecting with their surroundings in an increasingly complex and fast manner that will continue throughout their entire lives.

You’ll be amazed how quickly your bundle of joy opens their eyes to the world, suddenly discovers a toe, or starts babbling, and that’s where parents come in! Your baby relies on you and your support system to help them adjust to the outside world, because living inside the womb is all they’ve ever known. Let’s consider the characteristics of the maternal-womb: the thermostat is reassuringly regulated at 37 degrees Celsius, the baby is permanently surrounded by softness, is in constant physical contact with the mother, and soothed by her heartbeat and the rhythm of her daily movements. The uterus is very gentle with the baby’s nascent senses: there are no bright or flashy lights, no scents in this aquatic environment, and they have never experienced hunger, loneliness or had to lie on their back to sleep. So, it’s understandable that some newborns might be unable to sleep outside their mother’s arms.

A group of researchers on early childhood from the University of South Florida recommend parents to take into account that a period of adjustment is taking place after birth. Empathizing with the newborn’s sudden encounter with the world can help them attune into their needs. Dr. Karp suggests living the first months after pregnancy as if your baby was still in-utero. Promote skin-to-skin contact, hold them in fetal positions, allow them to feed on demand, let them use sucking for comfort, rock them with rhythmical movements or sounds, and spend as much time as possible with your baby close to your body, like in babywearing.