3 Week Old Baby: A Development and Milestones Guide

As new parents, it might be difficult to get a decent night’s rest when your precious 3-week old baby keeps crying. However, that’s the only way your baby can communicate with you right now. You might feel exhausted and frustrated for now, but remember that your newborn won’t stay small forever. Let’s see what 3-week old baby development milestones are in store for your little one.

3 Week Old Baby – Physical Development

By the third week, your baby’s skin should be peeling less and looking more plump, pink and clear. Don’t worry if your baby still has cradle cap – that rough scaly dandruff-like skin on his scalp – because most of the time, it will go away on its own. It might look unsightly and uncomfortable, but it won’t bother your newborn.

Your 3 week old baby would have also gained the weight they lost in his first week, and should continue to gain weight at approximately 25 grams per day. 

At this stage, your child’s median length and weight* should be as follows: 

• Boys
  – Length: 49.8 cm (19.6 inches)
  – Weight: 3.3 kg (7.4lb)
• Girls 
  – Length: 49.2 cm (19.4 inches)
  – Weight: 3.3kg (7.3lb)

And your child’s head circumference* should be:

• Boys: 34.5 cm (13.6 inches)
• Girls: 33.9 cm (13.3 inches)

As part of a 3-week-old baby development,  movements might be jerky and uncontrolled, which is normal for a newborn. This is because your baby’s nervous system and muscle control still need time to mature. In time, when their muscles get stronger, their movements will become more and more fluid.

How long should 3 week old babies sleep?

At 3 weeks old, babies typically sleep for varying durations, often totalling around 14 to 17 hours per day. However, their sleep patterns can be quite irregular and influenced by hunger, diaper changes, and other needs.

Newborns tend to sleep in shorter segments, ranging from 1 to 4 hours at a time, day and night. It’s important to remember that their sleep-wake cycles are still developing, so establishing a fixed sleep schedule might not be feasible just yet.

It is likely your baby will still be sleeping most of the time. Just make sure to put your baby down on their back to sleep as that is the safest sleeping position.

But during the short moments that your baby is awake, you can put them on their stomach to do some tummy time. This helps strengthen the neck muscles so baby can push up to sit, roll over and crawl in the later months.

Consult a doctor if your baby:

• Is still losing a lot of weight.

3 Week Old Baby – Cognitive Development

What should 3-week old babies be doing?

At three weeks, your baby is still trying to adjust to being outside of your womb. Loud noises will still startle them, trigger the waterworks and the Moro reflex. To help baby calm down and feel more secure, you can always try swaddling them. 

Another way for a baby to self-soothe is by sucking.  However, if you are nursing, you might want to wait until breastfeeding is well established before offering a pacifier so the baby can self-soothe. Even if you don’t offer a pacifier, sucking on their own fingers will also help your baby to self-soothe.

But did you know that you can also comfort your newborn by talking softly to them? Your little one can recognise songs or sounds heard when they were still in your womb and mum’s voice is one of the sounds they hear the most.

So continue to talk and sing to your baby, and even though they cannot understand you yet, you are already laying the foundation for language development. 

Try hanging a mobile in high-contrast colours or black and white over their cot. You’ll see your baby gazing at the mobile or tracking it with their eyes. 

Can a 3-week old baby smile?

Yes, it’s entirely possible for 3-week-old babies to smile! At this early stage, those sweet smiles are more likely to be reflexive or related to gas rather than in response to external stimuli. Babies are born with a “rooting reflex” that causes them to turn their heads and open their mouths when their cheeks are touched. Sometimes, this can create the appearance of a smile.

However, by around 6 to 8 weeks, you’ll start to notice more social smiles emerging as your baby becomes more aware of their surroundings and starts responding to your face and voice with genuine happiness.

Now it might seem as though all your baby does is feed, poop, sleep and repeat. But your baby’s brain is actually absorbing a lot of new things during this 3-week old baby development phase. 

A good way to help your baby learn is to put your face in front of them during tummy time. Allow baby to study your face and copy your lip movements. It might be very subtle, but if you watch them carefully enough you might actually notice him trying to copy you.

Right now, you baby’s main mode of communicating with you is by crying. While it might be frustrating at first trying to distinguish the different types of cry — hungry/ bored/ sleepy/ lonely/ over-stimulated, and so on — soon, you’ll be able to make those subtle differences. 

For now, try to rule out one cause at a time. Offer your breast, change baby’s position so they see a “new view”, gently rock them, change baby’s diaper or clothes. Hang in there mummy, you got this! 

Consult a doctor if your baby:

• Does not startle at loud noises.
• Does not cry at all.

Nutrition and Health

Breastfeeding should be well established by now, and your breasts might be full and heavy with milk. There is no hard and fast rule about when to nurse your baby. At this age, feeding on demand is still best. The best way is to take cues from your baby and feed whenever needed, as babies typically know exactly how much food they need.

As long as your baby is latching well, satisfied and gaining weight, then all is well. Check for lip and tongue ties if you have facing breastfeeding problems. You will still be able to breastfeed if your baby has a cleft lip or palate.

Also, remember to let the baby drain each breast at each feed so you don’t suffer from blocked ducts or mastitis. If for any reason you cannot breastfeed, then the only other suitable form of nourishment for your newborn is formula milk. 

Your baby needs around 368.7 calories a day. Typically, the amount of breastmilk/formula milk for your baby at this stage is:

• Breastmilk: 19.3-30.4 ounces/day
• Formula: 16 – 24 ounces/day

If your baby was already having colic problems before this, then it might probably still be there during this 3-week-old development phase. While it might be heartbreaking to see your little one so uncomfortable, this too will also pass. However, if it seems to be getting worse, the paediatrician might be able to offer some relief. 

Vaccinations and common illnesses

This week, there are no vaccinations due for your baby.  However remember that next week as your baby turns one month old, they will be due for the second dose of the Hepatitis B vaccine. To find out more about your baby’s vaccination schedules, please click here.

Your baby’s immune system is still very immature making them very vulnerable to illnesses like the common cold. While it may not be as much of a big deal in older kids, in a newborn, a common cold could lead to severe consequences.

Therefore, it is important to make sure that whoever handles your baby is practising strict hygiene which includes frequent hand-washing. Wear a mask if you have a cold or cough, and any other family members or friends with colds or who are sick should stay far away from the baby until they are better.

If your baby catches a common cold or other common illness, make sure that you bring them to the paediatrician immediately. At this stage, your baby is too young for any kind of home remedies. 

Finally, it is important to make sure that nobody—including yourself—ever kisses your baby on their face, mouth, hands or feet as this could potentially transmit the fatal HPV virus to your little one.

Consult a doctor if your baby:

• Seems to have trouble breathing, indicated by rapid breathing, flaring of the nose, grunting while breathing or bluish skin that refuses to fade. 
• Vomits constantly.
• Has white patches on their tongue, which could indicate oral thrush.
• Has even a slight fever (over 37 degrees Celsius). 
• Has trouble latching on to your breasts. 
• Has a bloated, highly distended stomach.

Newborn Care

Make sure you do not shake your baby especially when they won’t stop crying. Your baby’s neck is still very weak and cannot fully support their head. Shaking can cause your baby’s fragile brain to slide back and forth within the skull, possibly inflicting irreversible brain trauma also known as shaken baby syndrome.

Ensure that the room your newborn is sleeping in is of the right temperature. The ideal room temperature is 24ºC if you are using an air conditioner. At this temperature, baby’s body is not fighting to stay cool or trying to warm up.

At three weeks, your little one will still be sleeping a lot, regardless of day/night. But, it’s not too early to gently start teaching them about the difference between day and night. 

Try introducing a bedtime routine: bath, nurse, cuddle and sing/talk at the same time every evening. Do your last feed in a dark room with dimmed lights. With night-time feeds too, keep the lights dim and try not to engage your baby too much as you would in the daytime. Don’t expect changes to happen overnight, but over the months, your little one should start associating the bed-time routine with sleep. 

Continue to bathe your baby carefully, supporting their neck and back to prevent slipping. If you have a son, click here to read about how you should clean his genitals, and if you have a baby girl, here’s your article. 

Remember that you should never insert cotton buds (or anything else) in your baby’s ears to clean them. This could rupture baby’s ear drum or push the wax in further, creating health issues. 

Consult a doctor if your baby:

• If you notice any discharge from your baby’s genitals.
• If you or another caregiver accidentally drop your baby.

3 Week Old Baby: How to Spot the Danger Signs

Your adorable bundle of joy might be keeping you on your toes, and that’s totally normal. While most of the time things are just fine, it’s essential to know the red flags when they pop up. Here’s a quick list of red flags to keep an eye out for in your 3-week-old munchkin:

1. High Fever

2. Severe Jaundice

3. Difficulty Breathing

4. Lethargy or Extreme Sleepiness

5. Persistent Vomiting or Diarrhea

6. Seizures

7. Unusual Rashes

8. Difficulty Feeding

Remember, trust your instincts – if something feels off, don’t hesitate to reach out to your paediatrician for guidance.