The fourth trimester

We’re hearing more and more about the “fourth trimester” after pregnancy. What exactly is it and where did the concept come from?

What is the fourth trimester?

The fourth trimester is the 12-week period following the birth of a baby. It is a time of transition, both for the parents—especially the mother—and for the newborn, who needs a safe, warm, and intimate environment to adapt to their new life.

The origins of the fourth trimester

American author Jean Liedloff is one of the people who introduced the concept of the fourth trimester in the 1970s. After spending time among Indigenous communities in Venezuela, she came to the conclusion that for optimal development, babies need to be in conditions similar to those in which our species evolved. She found that this process follows a continuum, meaning a sequence of very specific experiences. The first months of life are therefore a continuation of pregnancy.

After they’re born, a baby still needs some of the elements that cradled them in the womb, such as physical proximity. Liedloff proposed this theory in her book, The Continuum Concept, where she advocates practices such as babywearing, co-sleeping, and breastfeeding.

This book was later a source of inspiration for noted pediatrician William Sears. In his books, Dr. Sears promotes parenting practices based on attachment theory that are very similar to those supported by Liedloff.

However, it was Dr. Harvey Karp who popularized the term fourth trimester in the 2000s. According to Dr. Karp, babies are born too early. This is why, in order to soothe them, it is necessary to imitate the environment of the uterus. Among other things, Dr. Karp recommends rocking your baby and meeting their need to suck. He also promotes swaddling, though experts recommend exercising caution with this practice.

These definitions of the fourth trimester are largely based on the baby’s experience. However, some health professionals associate the fourth trimester with the mother’s experience, as she needs to both physically recover from childbirth and adjust to her new role as a mother. Although these two perspectives can be complementary, they are rarely presented together.

That said, more and more experts now refer to the fourth trimester as a time when mother and child should be in the same bubble. For example, Ingrid Bayot, who trained as a midwife in Belgium and is now a perinatal coach in Quebec, published a book called Le quatrième trimestre de la grossesse in 2018. Her book seeks to raise awareness about the issues that affect both baby and mother in the months following birth. In particular, she emphasizes the idea that a newborn is a fetus outside of the womb, and that a mother’s body does not fully return to the way it was before, even though the characteristics of pregnancy disappear.

The fourth trimester for the baby

According to the idea that babies are born too early, a newborn can be compared to a fetus outside their mother’s womb during their first few months of life. This is why this period is referred to as a fourth trimester.

Some experts believe that pregnancy ends before the baby is ready to face the world. Because babies are born very immature from a neurological point of view, they are entirely dependent on their caregivers. This explains the strong relationship between a mother and her baby, who form an intimately bonded unit known as a dyad.

To help their baby adjust to life outside the womb, parents can use strategies that promote closeness with their newborn.

• Breastfeeding basics
• Skin-to-skin contact (French only)
• Babywearing (French only)
• Swaddling
• Co-sleeping (French only). See also our fact sheet on babies’ sleep between the ages of 0 and 3 months (French only).
• Understanding why babies cry

The fourth trimester for the mother

According to the mother-centred view of the fourth trimester, while the fetus becomes a baby after birth, it is also at this time that the mother must adjust to her new role. During this period, the mother adapts to her new responsibilities. From a physical point of view, she is also experiencing significant hormonal changes in addition to having to recover from childbirth, which may have been very demanding.

Here are some of our fact sheets that discuss the aftermath of childbirth and a mother’s adaptation to her new role.

• Postpartum recovery
• When childbirth doesn’t go as planned
• Postpartum depression
• Fertility and breastfeeding (French only)
• Becoming a parent (French only)
• Feeling like a good parent (French only)
• How to build confidence as a parent (French only)

The other parent and close family members can also help out.

• Paternity leave (French only)
• Becoming a father
• Sharing tasks between partners (French only)
• Communication between partners (French only)
• A new baby’s arrival: How to help out new parents (French only)

Things to keep in mind

• A baby is completely dependent on their parents for the first few months after birth.
• The mother must recover from childbirth and adapt to her new role as a mom.
• The father also needs to get used to the arrival of the baby.
• Family and close friends can support the mother, father, and baby during this transition period.

Scientific review: Louise Godin, graduate nurse and IBCLC lactation consultant Research and copywriting: The Naître et grandir Team May 2021

Photo: GettyImages/1134293514