Your 3 Week Old Baby: Changes To Look Out For

Jo Kingsley
Feb 29, 2024 By Jo Kingsley
Originally Published on Mar 03, 2021
At three weeks old, you can start to introduce some closely supervised tummy time.
Age: 0-99
Read time: 9.0 Min

Your newborn baby is already three weeks old!

Time is likely to be slipping by in a haze of adoration and (seemingly constant!) feeds, day and night. And you might now start to find yourself wondering if your newborn's development is on track.

There's so much to think about in that first year: weight gain, feeding, sleeping, physical and emotional development... It's easy to get lost down the rabbit hole of development research and health anxieties.

But Kidadl are here to help. Whether you're looking for advice on [10-week-old baby] milestones or [11-week-old baby] milestones as your baby grows, we're here with all the advice and support you need. Because we know that every baby is different and whatever concern you might have, there's usually absolutely nothing to worry about. You're doing a great job.

So if you need a little help and reassurance when it comes to 3-week-old baby milestones, 3-week-old baby sleeping patterns and more this article is for you.


Your 3-week-old is going to be doing a lot of sleeping. Baby should be getting anywhere between 14 and 17 hours of sleep (if not more!) in a period of 24 hours. In the first few weeks, baby is still likely to wake every two to three hours (or even less) during the night time for feeding, so they will still need plenty of naps during daylight hours. Baby's daytime naps are often a  good time for you to take a nap, too.

Newborn babies don't understand the difference between night and day and need a little help developing the internal body clock we all have that regulates our sleep, otherwise known as our circadian rhythm. Although your 3-week-old will still be sleeping during both the night and day, there are still some things you can do to differentiate the two and start to create a schedule. For example, including a relaxing bath, cuddle, and story as part of the night time bedtime routine, and keeping naps simple. You can also keep a curtain or blind slightly ajar at nap time, whilst ensuring baby's room is nice and dark at night time.

It might also be wise to make sure baby doesn't sleep too long during daytime naps. The old wives tale says you should never wake a sleeping baby, but sometimes it's better to ensure that each day time nap isn't too long if you want to encourage longer stretches of sleep at night. No longer than three to four hours is ideal.

Although there are no huge milestones when it comes to 3-week-old baby sleep patterns at week three (it might still be a bit hard going!), you as a parent are building your confidence and you and baby together are establishing a routine and a sense of trusted comfort.


At three weeks old, your baby will be taking around two to three ounces of milk per feed.

At 3 weeks old, the average baby stomach size is anywhere between the size of a kiwi and a large hen's egg. So your newborn will be taking around two to three ounces of milk per feed. And they'll need a feed, on average, every three to four hours. But it's important to remember that every baby is different, and your baby's feeding pattern may well look different to a friend in your parenting class.

A feed, and how your baby responds to it, will also look different depending on whether they are breast or formula-fed. Breastfeeding babies often take a little longer to feed and might take a little less breast milk each time, meaning they may well feed more often,  sucking at the breast is harder work than drinking from the fast-flowing teat of a bottle.

But at 3 weeks old, you will have probably already started to pick up on some of your baby's cues, although if you're unsure, you can always talk to your pediatrician or midwife.

Baby might be hungry if you see them sucking their fingers, tongue, or lips, mimicking that sucking action that they would use on a nipple or teat, or opening their mouth and slapping their lips. Breastfed babies, in particular, may nuzzle directly into chests to find a nipple (they're often not fussy about which chest they go for in their quest for milk!) or start what's known as 'rooting'. This is a reflex that sees them turn their head to the side, open their mouth and start to suck, as if they were at the breast.

If your new baby fusses after feeding, they may be suffering from gas, colic, or reflux, but it's also possible they didn't eat enough. Newborn babies are often prone to falling asleep, particularly at the breast, forgetting to eat, and then waking up hungry.

The amount of wet and dirty diapers your baby makes is a good indicator of how much they're eating, and can also help to illuminate any issues, such as constipation or diarrhea.

Weight gain is another method of assessing if your little one is eating enough, although there are quite a few variables when it comes to weight. Often babies who are breastfeeding gain weight slower than bottle or formula-fed babies, as it takes a while longer to figure out a good latch and establish a feeding rhythm. Babies should also only gain weight in relation to their own growth chart. For example, if they're small and on the 15th percentile, they don't need to suddenly jump to the 50th. If anything, that could mean they're overfeeding. Baby's weight gain and growth should rise steadily following the centile on which they measured during pregnancy and at birth.

If you have any concerns regarding your baby's growth, always contact your pediatrician.

Play & Movement

For your 3-week-old baby, development is still ongoing so play won't be too active just yet. They won't be able to hold anything too large or heavy, but items like rattles, ribbon wands, sleigh bells, rings, or textured toys are perfect for you to use with them. Baby will love the sound, it will help stimulate their eyesight, encourage them to reach out and grasp, and bring some wonderful one-on-one bonding time.

You can also start to introduce some closely supervised tummy time, on a soft mat and with the help of a tummy time support cushion, to help strengthen baby's neck and shoulder muscles and encourage them to lift their head. For the first month, they might not enjoy this sensation too much, so don't be worried if they quickly get frustrated or upset. A cuddle will fix it pretty quickly!

Play doesn't have to be active, either. Your baby will love listening to you read stories and sing songs; they will find comfort and joy in your voice. You could also try playing music for them, soothing lullabies are great for bedtime, but why not play something more up-tempo at playtime? If there was certain music you enjoyed playing whilst pregnant, why not try playing it again and see if they recognize it?

Your newborn will also love taking a walk with you in their buggy, looking up at the clouds in the sky, and listening to the birds in the trees. Or why not look out for a mother and baby screening at your local cinema? Baby will likely fall asleep and you'll get some much-needed grown-up time for an hour or two.


Your 3-week-old baby can only see around eight to 12 inches in front of them.

From birth, your little one can only see in black and white, in fact, they don't start to see in full color until around four months old. So books with pictures and patterns, especially dots and geometrics, in black and white are a great way to engage your little one. Three weeks is also a good time to start introducing toys with bold, primary colors to help stimulate baby's eyesight.

Along with having black and white vision, your 3-week-old baby's vision will also be nearsighted, meaning they can only see around eight to 12 inches in front of them. So make sure you're giving lots of close-up cuddles and letting baby get a really good look at your face (by three weeks old they will begin to be able to recognize your face now). And this is even more important for a 3-week-old baby, as their attention span is slowly starting to grow. It's still pretty short in the grand scheme of things, but it means the difference between a second or two, and baby holding your gaze as they look at you for up to 10 seconds. What a lovely milestone!

Anything Else To Look Out For

At three weeks old, crying is still your newborn's primary way of communicating. They cry if they're hungry, tired, gassy, or they just want a cuddle. If you can, try to start to distinguish between different types of cry. You will probably notice that their hungry cry is different from their cuddle cry, and this will help you to figure out how to soothe them by rocking, singing, or perhaps offering a pacifier, or whether a feed is needed instead.

It's worth noting that colic, when a baby won't stop crying, often without an obvious cause, can often begin around the week three mark. So if you're concerned, it's worth making a note of how often, and for how long, your baby is crying, as well as what you did to try and soothe them. You can then take this to a pediatrician who will be able to guide you further.

Babies can be fussy, but if you're struggling to comfort your newborn, do look out for other signs that they may be unwell. Crying coupled with frequent diarrhea or vomiting, constipation, excess gas, or a swollen tummy are all causes for concern and you should contact your pediatrician.

At this age, you might start to notice issues like cradle cap, a yellow-ish flaky skin on the scalp, or other mild rashes on their body. Most rashes are normal, as your baby gets used to life outside the womb. Try to avoid fragranced baby bubbles and oils, and use gentle and natural products where possible. Daily baths can also cause irritation, so cut down if necessary and just use a top and tail wash with a warm flannel to make sure baby stays nice and clean on non-bath days.

If baby has a persistent rash, always monitor symptoms and make sure to consult your pediatrician.

If you found this article helpful, then why not take a look at our [sample 2-month-old schedules] and [3-month-old schedules] for the future months to come?

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Written by Jo Kingsley

Bachelor of Arts specializing in Film and English

Jo Kingsley picture

Jo KingsleyBachelor of Arts specializing in Film and English

Jo is a versatile writer with a Bachelor's degree in Film and English from the University of Southhampton who is passionate about mental health and well-being, history, art, food and drink, and photography. As a work-from-home mom to two adventurous boys, she loves exploring local castles, museums, and galleries with them, and sharing her knowledge and interests through her blog.

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