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Your 12-Week-Old Baby
Updated on
September 11, 2023

Your 12-Week-Old Baby

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Your 12-Week-Old Baby.
Your 12-Week-Old Baby

End of the Fourth Trimester

Congrats! You made it (with the help of coffee) through the “fourth trimester.”

Your baby is finally starting to get the memo that life is pretty awesome outside of the womb and the swaddle. Thanks to major developmental milestones over the last few months, everyone is hopefully sleeping more, smiling more and getting out more.

The last few months have been a wild ride—full of ups and downs, tears (from both of you!), joy, stress and plenty of laughs (car keys in the fridge…again?). Just keep doing what you’re doing and be proud that you’re officially a pro at doing any and all tasks one-handed.

Try This: Keep the Convo Going

Talk to your baby a lot, make silly noises, sing and recognize their cues so you can encourage this adorable developmental back-and-forth. Even if it feels a little silly, narrate your day when you’re home with your baby by explaining what you’re doing, “It’s time for a nap now! I’m going to put you in your sleep sack and turn on the sound machine. And then I’m going to ignore the pile of dishes in the sink and watch The Crown until you wake up.” (Or something along those lines.)

Being exposed to new words boosts brain development and helps babies make sense of their new, exciting word. Plus, all of this conversation stimulates their emotional and social skills and makes them feel loved.

Milestone: “Smile Talk”

You don’t have to exchange any real words to have a great conversation with your baby. Around three months, your kiddo will be a pro at “smile talking,” which means a lot of back-and-forth grins between the two of you (so the next time you’re changing a massive diaper blowout in a public bathroom, you’ll hopefully get a smile when you need it most). There will also be plenty of giggles, gurgles and excited movements, too. They’ll be studying your face closely and may even mimic your expressions.

Doctor’s Corner: What’s with Percentiles?

Percentiles. You’ve been hearing this word a lot since your little one was born. Here’s why they’re important: your baby’s pediatrician uses a growth chart (based on gender and data compiled from diverse populations) to track weight, height and head circumference at each well-baby visit. Based on the numbers, your child will fall within a certain percentile.

So, let’s say your baby’s weight is in the 75th percentile. That means 25 percent of babies their age weigh more and 75 percent weigh less.

Whether your tot is in the 20th percentile or the 90th, doctors want to make sure your baby is continuing to follow along their own curve (paralleling one of the various percentile lines on the chart) and growing at a predictable, steady rate. So don’t get stressed out about the specific percentile number. It’s more about the rate of growth.

Growth charts set patterns and give insight into underlying issues. For example, if your baby has consistently been in the 50th percentile for weight, and then suddenly drops down to the 10th percentile, then that’s a sign for your pediatrician to investigate the reasons behind this significant weight drop.

Or perhaps your baby is getting taller, but their weight isn’t rising proportionally. This may be a sign to increase the amount they’re eating throughout the day so they catch back up.

Keep in mind: growth isn’t always a perfect science. Factors like growth spurts, feeding strikes and illnesses can impact growth rate.

For the first 24 months, doctors use the World Health Organization growth chart. Here’s more info on how it’s used.)

Growth Spurts: How’d You Get So Big?!

Babies go through a bunch of growth spurts during the first year. Although they can happen at any time, a three-month growth spurt is common.

Aside from needing to buy new bodysuits at a moment’s notice, other signs of a growth spurt can include: more sleep than usual (hallelujah!), less sleep than usual (eek!), some extra fussiness (in part due to restless nights) and an increase in hunger (hello, again cluster-feeding!).

If you’re breastfeeding, be sure to up your own water and food intake so you don’t get dehydrated or low on energy as you keep up with your growing kiddo.

Growth spurts can last anywhere from one day (yep, they may actually grow overnight!) to a week or so. And no matter how cranky your baby may get from all that growing, just remember, this too shall pass.

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