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The Fourth Trimester: what is it and how can you get through it?

When you google the term ‘the fourth trimester’, many blogs or parent-support websites will pop up. However, barely any research exists regarding the subject, which unfortunately leaves parents in the dark when it comes to evidence-based research regarding the matter. Let’s see what we can find in research about the first three months of a baby’s life.

The fourth trimester is a term brought into the world by Harvey Karp, and is used to describe the first three months of a baby’s life outside of the womb. It is often characterized by:

-long periods of crying with seemingly no reason to (fed, changed, not in pain, not too cold or hot…)

-inability to sleep in the basinet

-need for physical contact at all times

-only comfortable when being (breast)fed; will protest when being moved


All infants are born prematurely

Compared to other primates, the human infant’s brain is the most immature when born. There is no conclusive reason for this, but some researchers claim that, when humans started walking up, their pelvis changed and the outlet became smaller. Therefore, we could no longer birth our infants after a certain period, as their head circumference became too big for our now smaller pelvis. This resulted in babies being born prematurely, and with an underdeveloped brain. Now you can see why the first three months are being called ‘the fourth trimester’, or an extension of pregnancy. A newborn’s brain still needs to go through extensive maturation.


Sleep hormones

All organisms have biological rhythms. We often talk about our biological clock; a finely tuned combination of hormones that start to rise from 7 pm onwards, peak around midnight, and diminish towards the morning. Light has an enormous effect on the production of these hormones. Joseph et al (20) were able to show in their research that newborns don’t start secreting the necessary hormones to have a circadian rhythm (which means as much as sleeping at night and being awake during the day) until around 8 weeks. At this age, cortisol levels start changing and over the next few weeks, melatonin followed suit, together with deeper sleep and changes in body temperature.

What this means for a newborn baby is that their sleep pattern is still very immature. Where an older baby will cycle through sleep phases that resemble an adult’s in length, a newborn will seemingly switch between deep and light sleep in minutes.


Infant positioning

The medical world hates not being able to fix a problem. So whenever a new mother presents herself with a crying newborn, many doctors rush to come with diagnoses like colics, allergies, insufficient milk production, and many more. Yet, even without intervention, many parents report their infant’s crying significantly dropped after three months. Science still doesn’t know why infants cry so much during the first three months, but the accelerated rate with which their brains develop probably has something to do with it. Adjusting to life outside of the womb also often gets addressed. During life in utero, a fetus is oriented vertically (be it feet up or head up), surrounded by warm fluids, with a shimmer of red light shining through the mother’s skin and tissues, and the sound of blood pumping through her veins and organs working as background music. When born, an infant is placed on his back in a crib, where it is cold, dark and silent. Kahraman et al (2018) carried out a study which showed that infants who were placed on their tummy, nested in with linen, produced less cortisol (the stress hormone) when receiving a prick in the heel. Overall, their sleep was also deeper, and babies were also better to self-regulate after going through a light sleep phase. Many parents will recognize this as their newborn baby will only sleep on their chest. Where the skin-to-skin contact is also soothing, it is also the placement in prone position which helps a lot. Researchers attribute this to another remainder of our ancestors: our tummy is our most vulnerable body part, with many vital organs and no bony structure to protect them. Sleeping with an exposed abdomen would be less safe, resulting in an uneasy feeling this day and age.


Daily life implementations

Many blogs will give little tips on how to get your baby to sleep better, but it seems like better education regarding normal infant sleep is also necessary. Many parents are unaware of the immature brain of a newborn, and how it takes on average ten to twelve weeks for an infant to start producing the necessary hormones to build up a circadian rhythm. When parents know what to prepare themselves for, the fourth trimester could be less tiring. Parents should try to prepare themselves as good as possible for the irregular patterns that is newborn sleep. Here are some tips to try and make the adjustment period easier:


-do all your light and heavy reading regarding baby sleep in your third trimester. Nobody has the capacity for infant sleep books when they are running on 4 hours of sleep

-accept all the help you can get and, however cliché it may sound; sleep when baby sleeps. Get family, friends, grandparents, doulas and night nurses involved to hold baby during the day, so you can catch up on sleep. Outsource as many household tasks as you can. Order food, let visitors bring casseroles instead of cute baby pajamas’, get a cleaner or have your mother help with the laundry. As the newborn needs to be cocooned and showered with attention and assistance, so should the mother (and father).

-talking about the father: take turns on who sleeps with the baby. If you can, go and sleep in another room when it is not your turn. If you are breastfeeding, let your partner bring the baby over to the other room, and nurse lying on your side. There is 12 hours to be divided under the two of you; take good use of them.

-don’t feel forced to spend a fortune on fancy gimmicks that promise to help your baby sleep better. A muslin swaddle cloth works just as well as some expensive sleep sack. There are apps on your phone that can produce white noise. You can fabricate a nice, cozy nest for your little one with rolled up towels (just make sure there is no loose bedding close to your baby’s face). Anything that might stimulate the warm, cozy feeling from in the uterus can help.

-it might be a good idea to invest in a (gentle) sleep education course to prevent implementing practices to help your baby fall asleep, that you will have to wean them off of. Consider this before you give birth.

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