Peds, part 7: G&D - Infant Growth, Fontanelles, Dentition, and Reflexes

by Meris Shuwarger BSN, RN, CEN, TCRN December 20, 2021 Updated: August 09, 2023 5 min read

In this article, we discuss the normal growth and development milestones and expectations for the infant, which is from birth to one year.

The Pediatric Nursing series follows along with our Pediatric Nursing Flashcards, which are intended to help nurses and nursing students learn and retain information about caring for pediatric patients. The flashcards are a clear, complete study tool and a helpful reference for practicing RNs, PNs, and other medical professionals.

Cool Chicken When you see this Cool Chicken, that indicates one of Cathy's silly mnemonics to help you remember. The Cool Chicken hints in these articles are just a taste of what's available across our Level Up RN Flashcards for nursing students!

Infant physical growth and development (birth – 1 year)

From birth to one year of age, infants attain various anthropometric milestones in growth and development, that is, how their bodies change and what measurements we are likely to see.

Infant weight

When an infant is born, they initially lose weight. This is normal. The expected loss is up to about 10% of their birth weight. As they start to breastfeed or have formula feedings, infants start to gain weight again. Within about 1 week, they should be back to their birth weight.

By the time a child is four to six months, we expect to see that they have doubled their birth weight. By 12 months, their weight has tripled.

Infant length

In terms of length, we would expect to see an infant increase their length by approximately 50% in the first year. The child’s length increases about 1 inch per month in the first 6 months, then about one-half inch per month in the second 6 months.

Note that this measurement is not a height measurement — in order to have height, you have to be able to stand. Length is for measuring the child horizontally, when they are lying down.

Infant head circumference

Head circumference is another anthropometric measurement that is assessed during a child’s pediatric appointments. The normal head circumference of a full-term infant is 32 – 38 centimeters. At this point, the infant is a “pumpkin on a broomstick” — their head is going to be about two-centimeters larger in diameter than their chest. This is normal; at approximately one year of age, these measurements will even out, and the head and chest circumferences will be the same.


The fontanelles are the soft spots in the skull that allow an infant to pass through the birth canal, allowing for molding — for the bones to be compressed and overlap — part of helping to squeeze the baby’s big head through the birth canal. After birth, fontanelles begin to close on their own.

The posterior (rear) fontanelle closes between 6 and 8 weeks.

The anterior (front) fontanelle closes between 12 and 18 months.

Cool Chicken Just as baby is on her back first then turns onto her front later, posterior (back) fontanelle closes first then anterior (front) closes later.

If a fontanelle does not close at the right time, this could lead to health issues, which will be discussed later in this series.


Dentition, the way teeth develop, is another milestone (or set of milestones) in an infant’s development.

While there are no strict timelines for dentition, an infant’s first tooth typically erupts or begins to appear in the gum line at about six months. The first teeth to emerge are usually the bottom front teeth followed by the top front teeth.

The rate of dentition for infants is approximately 6 – 8 teeth by 12 months and a total of 20 deciduous (baby) teeth by age 3.

When it comes to guessing a child’s age, our Cool Chicken hint is a good way to figure this out.

Cool Chicken Age of child in months - 6 ≈ total number of teeth (up to age 24 mos).

Consider a scenario in an emergency room where you are treating a child who has been in a car accident and the parents are being cared for in another facility — how do you figure out the age of the child? Counting their teeth is one way to approximate their age.

So, for example, if the child has six teeth, they are probably around 12 months old. Per our Cool Chicken equation (working back-to-front): 12 (months) minus 6 equals 6 (the number of teeth counted in the child's mouth). The child is approximately 12 months old. Note that this method of calculation only works until the child turns two.

Infant reflexes

At birth, infants display a range of normal, primitive reflexes that are crucial for the baby’s survival — involuntary muscle reactions due to physical stimulation or other triggers: sound, light, sudden movements, and being stroked or touched. These disappear over time as the child ages and their central nervous system matures.

Below is a list of infant reflexes, what they are, and when they usually disappear.

Moro/startle reflex

The Moro or startle reflex is the infant’s response to the sensation that they are falling (they feel a lack of support). It can occur when an infant hears a loud noise or experiences a sudden movement. The infant will extend their arms then bend and pull them in toward the body with a brief cry. This reflex disappears at around 2 mos.

Walking/stepping reflex

If an infant is held up (supported) and their feet touch on the ground, they will make a stepping motion. This is a protective reflex. (Remember, they cannot support their weight yet.) This reflex disappears at around 2 mos.

Rooting reflex

Rooting is the reflex of looking around for food. For an infant, it means looking for the mother's nipple in anticipation of breastfeeding. This reflex is triggered if their face is stroked — they will turn their head in that direction and open their mouth, looking for food. This reflex disappears at around 4 mos.

Sucking reflex

When its lips are touched, an infant begins to suck. Note that premature babies may have a weak sucking reflex. This reflex disappears at around 2 mos.

Palmar grasp reflex

When something (e.g., a finger) is placed in the baby’s palm, the infant closes their hand and grips it. This reflex disappears at around 5 – 6 mos.

Tonic neck reflex

Also called “fencing position,” this reflex occurs when the head is turned. The infant extends the arm and leg on the same side, while the opposite arm and leg flex inward.This reflex disappears at around 5 – 7 mos.

Cool Chicken Fencing position!

Plantar grasp reflex

Similar to the palmer grasp, the plantar grasp reflex occurs when the sole of the foot is touched near the base of the toes, causing the infant to flex or curl their toes. This reflex disappears at around 9 – 12 mos.

Babinski reflex

In a Babinski reflex, when the lateral plantar aspect of the foot is stroked (usually in the shape of an upside-down “J”), the infant’s toes dorsiflex and fan outward (the toes pull up and fan out). Infants display a positive Babinski reflex until 12 months.

Note that in an adult, this reflex is a cause for concern, as it may indicate an underlying issue in the central nervous system.

Full Transcript

Hi, I'm Meris with Level Up RN, and in this video, I'm going to be talking to you about some normal growth and development milestones and expectations for the infant, which is birth to one year. I'm going to be following along using our pediatrics flashcards. I'm starting here in the growth and development section. If you have a set of your own already, I would invite you to follow along with me. And if not, check out our website, where you can grab a set of your own. All right, let's get started. Okay, so first up, we are talking about some anthropometric milestones in growth and development for infants, and that means that we're talking about how their body changes and what those measurements are that we expect to see. So you'll see here, we've got something here in bold red text, which means that we think it's pretty important for you to know. But there's a lot more of information on this card. So let's talk about it.
When an infant is born. They initially actually lose weight and that is normal and expected up to about 10% of their birth weight. That's something that we expect to see. However, we expect that the child should be back to their birth weight by one week of age, so they should lose weight initially. And then they're going to start breastfeeding or having formula feedings, and then they're going to start to gain weight again. So we should see that by one week, they're back to their birth weight. However, by the time a child is four to six months, we expect to see that they have doubled their birth weight. So let's make up a number, the child is born at seven pounds, between that four to six-month range, we're expecting the child to be 14 pounds, right? So that's just a general guideline. If we didn't see that being met, that might be something that we investigate further. We also expect that by one year of age, at 12 months old, a child should triple their birth weight. So that seven-pound infant at a year old should now be 21 lbs. Okay. It's just math, right? It's not too bad. You just have to memorize those numbers because that does come up a lot in clinical practice in terms of, "Is my child meeting those guidelines, those milestones?" That's one of the big ones that we're going to be looking at.
Now length, we would expect to see that-- within the first year, they're going to increase their length by 50%. Why don't we call it height? Height is for when you are able to stand to be measured. Length is four when we do it horizontally. And then we would say that for the first six months of their life, they're going to gain about one inch per month and then a half an inch per month in the second six months. Again, it's just a general guideline, not hard and fast, but that's kind of what we expect to see. Now, head circumference, remember that we do measure this as part of those anthropometric measurements at a child's pediatric appointments. So the normal head circumference of a full-term infant is going to be 32 to 38 centimeters. And remember, these are pumpkins on broomsticks. So we expect that their head is actually going to have about a two-centimeter larger diameter than their chest. That is normal. We would never-- if my head were two centimeters larger than my chest circumference, I would look like a cartoon character, right? So this is normal for children, okay? Very important to understand that that is a normal finding. It will go away with age, though. And the head and chest circumference will be equal to one another approximately at one year of age.
Okay. Let's keep on chugging right along. We are now moving on to talk about fontanelles. If you remember, we talked about fontanelles. Those are those sort of soft spots in the skull that allow an infant to pass through the birth canal because it allows for molding and kind of for those bones to get squished over top of each other, things like that. Because it's hard to squeeze a big head through a birth canal, right? Fontanelles help us there, but they don't stick around forever, right? I don't have a fontanelle anymore. That would be really bad. So let's talk about when they close. This is important because if they don't close at the right time, then we can end up with some problems and you'll see those when we talk about it in the alterations of health videos. But right now, let's just talk about the normals. So posterior fontanel, this one back here is going to close between six to eight weeks. Okay? Six to eight weeks. Anterior fontanel This one up front is going to close between 12 to 18 months. Okay? Big difference in when they close. So we have a cool chicken hint here on the card. Remember, the cool chickens are how we think that you might be able to remember these things. Little memory tricks. So we say, "Just as baby is on her back first, then turns on to her front later, posterior fontanel closes first and then anterior fontanel closes later." I also remember that around that 12 to 18-month range is when a child tends to start walking, and I think about a child falling when they're walking and hitting the front of their head. And that's kind of how I remember that that's around that same age. I don't know if that helps you, but that's how I remember it.
All right. Teeth. Teeth are an important thing to talk about. They are a milestone as well. So the first tooth typically erupts or starts to show up in the gum line at about six months. It's not hard and fast. It's a general guideline. My daughter didn't get her first tooth until she was nine months old. My son got his at five months old. It's just kind of in that general area. So typically we start with the bottom two teeth here and then move on to the top two teeth. But the infants will have all of their baby teeth by age three is kind of the thought here. Will have six to eight of them by age 12 months. All of them by age three. They've got a lot of teeth to fill in. It takes time. It's hard work. But you'll see here we have another cool chicken hint, and this one is very important when it comes to guessing a child's age. If you can think about maybe being an emergency room nurse or a pediatric ER nurse, and maybe you have a child who was in a car accident and the parents are being cared for in another facility, you don't know how old this child is. We have a lot of ways that we can estimate a child's age. But one of them is teeth. So you'll see here our cool chicken hint says,
"The age of the child in months minus six should approximately equal the total number of teeth that that child has up to age 24 months," right? So that's an important distinction there. It only works until they're two years old. So that means that if I have, let's say, a 12-month-old child, I would expect that they're going to have six teeth. Again, it's not hard and fast. It's just a guideline. But it can help you to say, "This child is around 12 months old." So if I look in their mouth, they have six teeth. I'm going to say 6 plus 6, 12, that they're probably about 12 months old.
Okay, moving on. Let's talk here. Oh gosh. We have these amazing charts here for you of all of the different reflexes that you have because there's a lot of reflexes you're born with that don't stick around forever. So in these tables, we have the name of the reflex, the age at which it should disappear and then a description of that reflex. First up is the Moro or startle reflex. That's when an infant hears a loud noise or a sudden movement like if you bump into their crib or sometimes they get the sensation of falling, they will put their arms out, bring them back in, and cry. That is called the Moro reflex. Walking or stepping, if I hold an infant up and have their feet touch on the ground, they will kind of make a stepping motion. It's a protective reflex. They can't actually support their weight, though. Rooting. Rooting is the reflex of looking around for food, so essentially looking for a nipple, right? For breastfeeding. And this is going to be that the child, when their face is stroked, they're going to turn their head in that direction looking for food. Sucking reflex, this one is going to be when the lips are touched, the infant begins to suck. Now, Moro should disappear at two months along with the stepping reflex, and then rooting and sucking should disappear at four months old.
Okay, the last one here, this is more reflexes, palmar grasp. That means when I put something in the palm of the baby's hand, they're going to close their hand and grip it tightly. So very commonly this is someone seeing a newborn and they put their finger here and they grab on so tight and they say, "Oh my gosh, she loves me so much." I hate to break it to you, it's a reflex. Okay, that should disappear by five to six months. Tonic neck reflex. This is sometimes called fencing position, so this is when the head is turned, the infant is going to extend the arm and leg on the same side, while the opposite arm and leg are going to flex inward. So basically, if you turn my head this way, this arm and leg are going to go out and this one is going to come in. And this is kind of fencing positioned, right? If you've ever seen fencers. So that one should disappear by five to seven months. Plantar grasp, same as palmar grasp, except the sole of the foot, disappears between 9 to 12 months. And Babinski reflex. Remember, Babinski reflex, we should expect to see a positive Babinski sign up until age 12 months. In an adult, this is an ominous and very bad finding. In a child under the age of one year, this is a normal finding. So when the sole of the foot is stroked in an upside-down J, we're going to see the toes are going to fan out and dorsiflex, they're going to pull up and fan out. That is normal.
All right. I'm going to ask you some quiz questions to test your knowledge of some key facts I provided in this video. Okay, so you are caring for a child who weighed six pounds, two ounces at birth. They're in your clinic today for their six-month checkup, what do you expect their weight to be? So the pediatrician informs a child's caregiver that their six-week-old infant fontanelle is beginning to close, which fontanelle is the provider likely referring to? You're assessing a child and you note that they have 12 teeth. Based on this information, how old do you presume this child to be? You observe that when you place your finger in the palm of a four-month-old child that they close their fingers around it and grab it tightly. Two questions here. What is the name of this reflex and is it normal for this four-month-old to be displaying it? All right. Let me know how you did in the comments, I'm excited to hear how you managed on those quiz questions. Thanks so much and happy studying.

Leave a comment

Comments will be approved before showing up.