Everything You Need to Know About the 4th Trimester

Verywell / Julie Bang

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While new parents prepare in many ways for the baby they are about to meet, they often find themselves feeling surprised by how disorienting and overwhelming caring for a newborn actually is. Although there is certainly joy, the first few months can feel fragmented, unbearably exhausting—and the relentless needs of a newborn can make parents feel like they never get a break.

You can blame much of this on a little phenomenon called the fourth trimester. The idea is that the first three months of a baby’s life are like another "trimester" of pregnancy because in many ways newborns are still gestating, even after they are born.

Your baby’s constant need to be held, carried, and fed isn’t your fault—it’s just how babies are. The silver lining is that while the fourth trimester can be very challenging, it is also the first chance to truly bond with your new baby.


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What Is the Fourth Trimester?

The idea of the fourth trimester is usually attributed to pediatrician and author Harvey Karp, MD, who described the concept in his book, "The Happiest Baby on the Block." Karp’s theory is that human mammals, unlike other mammals, are born fundamentally helpless.

For example, most mammals are able to walk soon after birth, but it takes most humans a good year to master that skill. Here are a few other things to know about Karp’s theory:

  • The reason humans are born “early” is because if we gestated longer, our heads would be too large to fit through the birth canal.
  • Thus, human babies are born essentially before they are actually ready to be born, which means they require a lot more attention and care than most mammals do after birth.
  • Not only are babies not fully developed yet, they are born “missing the womb,” and much of their fussing and neediness has to do with a feeling of disorientation and an inability to self-soothe without assistance.
  • Many newborn behaviors—such as a constant need to be held, fed, rocked, and shushed—stem from the fact that babies are still adjusting to life outside the cozy and familiar quarters of their mother’s womb.

Overview of the Fourth Trimester

During the first three months of life, your baby will be doing a lot of growing, changing, and developing—all while needing a lot of extra attention from you. At the same time, if you are a new mom recovering from childbirth, your body and mind are going through enormous changes as well. All of it can be a lot to process, which is why it’s really helpful to understand what is normal and what to expect.

What’s Happening With Your Baby

During the first three months of life, your baby goes from being a tiny peanut who can’t lift their head or see anything more than a few inches in front of them, to a cooing, smiling baby who is getting ready to roll over for the first time.

  • Newborns may appear cross-eyed at times, and can only see about 8 to 15 inches in front of them. They also can't clearly see colors, and prefer black and white images. They also love to look at human faces, and by one month, they can recognize their parents' faces. By three months, your baby will able to follow a moving object across the room.
  • Newborns are basically a ball of instincts, with their movements and reactions largely controlled by primitive newborn reflexes. By 3 months, their movements become more active and deliberate, they smile responsively, and their begin to become social creatures.
  • Newborns can’t lift their heads, use their hands deliberately, or control their body movements much. By 3 months, newborns can usually raise their head and chest while lying on their tummies, take swipes at moving objects, and meaningfully bring their hands to their mouth.

What’s Happening With You

Most people focus on what is happening with babies during fourth trimester, but moms are experiencing a birthing on their own, and in many ways are orientating themselves to their brand new life and identity.

This process can be difficult for many women who often need just as much TLC as their babies do.

  • In the fourth trimester, moms are recovering from childbirth, and may be experiencing soreness, cramping, healing of wounds, and will experience several weeks of postpartum bleeding. It can take weeks or even months for your body to feel totally normal again.
  • There is a major hormonal upheaval experienced by moms in the first few weeks after birth, because their bodies are shifting from the onslaught of pregnancy hormones to a more normal hormonal make-up. This can cause mood swings and what is often dubbed “the baby blues.” These blues usually resolve within 10 days of birth.
  • If you are experiencing mood swings that last beyond the first 10 days postpartum, or that are making it difficult for you to function normally, contact your healthcare provider, as you may be experiencing a common, treatable postpartum mood disorder, such as postpartum depression or postpartum anxiety.
  • If you are breastfeeding, you may experience engorgement, sensitive or tender nipples, and middle of the night leakage. Most moms experience at least one of these. Ask to see a lactation consultant before you leave the hospital if your nipples are very sore when nursing, to check your baby’s latch is good. If you are still experiencing pain or other problems while breastfeeding after a few days at home, seek help from a lactation consultant or breastfeeding support group.

Hallmarks of the Fourth Trimester

Every baby is different, and some don’t seem as bothered in the early going as others. Still, all babies are going through an adjustment in the first few months of life.

The womb was a safe, cozy place where all their needs were met. They are thrust into a sometimes cold, chaotic world with sounds, smells, and sensations they’ve never experienced before.

Now, all of a sudden, they are experiencing things like hunger, thirst, coldness, heat, digestive rumblings, and fatigue. And yet, they don’t have any way yet to communicate their needs. It’s tough being a newborn. Here are some things you can expect from your little cherub.


Crying and fussing is very common during the first three months of life. What’s difficult about it is that parents often have trouble figuring out what their babies are crying about. Sometimes you go through the litany of possible reasons—hunger, needing a diaper change, needing to be burped, overstimulated, etc.—and you figure out the cause. Other times, you are left dumbfounded.

Crying usually peaks around five to six weeks of age, and is often more frequent in the evening. Some babies develop colic, which is defined as crying three or more hours a day, three days a week, and for at least three weeks. If you have any concerns about your baby’s crying, contact your pediatrician.

Help, I Can’t Put My Baby Down!

In the womb, your baby was constantly held, curled up, and in constant contact with mommy. It takes a while for a baby to be comfortable outside the arms of a parent or other loved one. If your baby cries anytime you put them down, you may think you have done something wrong, or that they will never be independent.

Rest assured, this behavior is totally normal and common. Before you know it, your little toddler will be running away from you in the playground and you will have trouble keeping up.

Immature Sleep

Just like everything else, your newborn’s sleep isn’t mature yet. At first, it’s normal for a newborn to sleep much of the day, and be wide awake at night. Again, this has to do with the fact that when they were inside the womb, they were lulled to sleep by your walking during the day, and were likely up all night partying when you finally stopped moving and tried to sleep.

By about six weeks, your baby’s circadian rhythms have become more mature and they should do more of their sleeping at night. But your baby’s sleep patterns are still erratic, and they spend much of their time in REM (active) sleep.

You shouldn’t expect much in the way of a schedule yet. And while sleeping through the night may come in a few months, right now it’s perfectly normal for your baby to be up frequently at night.

Irregular Feeding Patterns

Babies' stomachs are the size of their little fists, so you can’t expect them to eat very much at once; frequent, small meals are normal and necessary. During the fourth trimester, your baby is going to eat every one-and-a-half to three hours, including in the middle of the night, and they may not always eat on a set schedule.

Especially if you are breastfeeding, it’s important to feed your baby on demand so you can keep up your milk supply and not get too engorged. Sometimes you will notice that your baby seems to want to eat constantly for a few days.

This "cluster feeding" is probably due to a growth spurt, which happens every few weeks during the first three months. Infant feeding can be exhausting, but it will become a little less frequent and more predictable over the next few months.

How New Moms Can Cope

As you read about what the fourth trimester is all about, you might be thinking: “Well, it may be normal, but how am I going to get through this?” Just because your newborn’s behavior is normal and expected doesn’t mean that it won't be difficult to manage at times. Fortunately, there is actually a lot you can do to try to soothe your baby, decrease their crying, and make life a little easier for your baby and yourself.

Remember, too, that anyone can participate in these tasks, from your partner, to a grandparent, and even an older sibling.


Babies were used to being squished into a cozy little fetal ball in the womb. Placing your baby safely in a baby carrier like a sling or wrap can help mimic the feeling of the womb. Make sure the carrier you use is made for newborns and supports your baby's neck. Once your baby is secured in the carrier, check that they can breathe and that their mouth and nose aren't blocked.

An added bonus is that babywearing can leave your hands free to do things like eat a meal—just avoid hot foods and drinks that could fall on and burn the baby. You also can read a book or scroll through your phone. (No guilt here: We all need breaks).


Like babywearing, swaddling your baby makes your baby feel more safe, secure, and soothed. You can learn the ins and outs of swaddling yourself, or invest in a swaddle blanket that can help you get the swaddle just right.


Your baby loves to be carried or rocked. After all, constant movement was the status quo when they were in the womb. Take your baby on a walk outside and you will probably find that both of you relax a little. You also can rock your baby in a glider, or sit on an exercise ball with them and do some gentle bouncing.


Babies have a strong sense of smell and a high need to be touched and held, so they love to be held directly against your skin, listening to your heartbeat, and feeling your breath. There is almost nothing sweeter than having a little skin-to-skin time with your newborn, and it can also be a great aid to breastfeeding, as it taps into your baby’s natural breastfeeding instincts.

Parent Self-Care

The fourth trimester is not all about the baby, though. Getting through this period means making sure you are able to practice self-care, too. This can be challenging, but sometimes self-care simply means having grandma hold the baby for an hour while you nap alone, take a shower, or even go to the grocery store alone.

You can figure out what works for you and your life, but it's important to make self-care a priority, because caring for a newborn is a tremendous task, and you can’t pour from an empty cup.

A Word From Verywell

In a few weeks, as you watch your baby grow and change in amazing and miraculous ways, the fourth trimester will feel like a distinct memory of the past. When you’re in it, though, you may feel that each day lasts a million years and that you will never be out of the stage when your baby needs this much constant care and attention.

Remember that these days of constant neediness are perfectly normal, and that they will pass before you know it. Keep in mind, too, that you are not meant to do this alone, so accept any help that is available, and ask for whatever help you can. If you have any concerns about your baby’s development or your own mental or physical health during the fourth trimester, don’t hesitate to reach out to a health professional for guidance.

As difficult as may be to imagine, you will actually miss the days when your baby wanted nothing more than to be snuggled up against you 24/7. So, take a few moments to soak it all in, sneak in a few extra cuddles, and breathe in the scent of that delicious newborn head.

Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Wendy Wisner
Wendy Wisner is a lactation consultant and writer covering maternal/child health, parenting, general health and wellness, and mental health. She has worked with breastfeeding parents for over a decade, and is a mom to two boys.