It's easy to be obsessed with a child's weight. Parents want to make sure their baby is "normal" and healthy. Weight measurements in pounds and ounces are simple to get, shareable, simple to understand, and something we can all relate to.
However, the baby's average weight is also a cause for concern. I've never met anyone who didn't worry about their baby's weight at some point. So, let's take a look at what counts as average birth weight, how and when a baby's weight changes, and how percentiles work.
What Is the Average Baby Weight at Birth?
The average birth weight of the newborn in the United States is approximately 7.5 pounds. Any birth weight between 5.5lbs and 10lbs is considered normal. This healthy average weight range applies to babies born between 37 weeks and 40 weeks and 6 days.
How Big of a Baby Can You Deliver?
A baby with a birth weight greater than 8 lbs 13 ounces is considered large. About 9% of children fall within this range. The risks to both the baby and the mother increase significantly when the birth weight is above 9 pounds and 15 ounces.
However, how big a baby you can give birth doesn't just depend on your baby's weight. It also depends on:
- The position of your baby during labor.
- The strength of your uterine contractions.
- How big is your baby in relation to the size and shape of your pelvis.
A woman with a larger and wider pelvis may be able to vaginally deliver an older baby than a woman with a smaller, narrower pelvis. Only a doctor can advise if your baby's size could be causing problems during vaginal delivery.
Factors Affecting Average Baby Weight at Birth
A baby's birth weight is the result of a complex combination of factors. To complicate matters further, there are no hard and fast rules as to how, or if, any of these factors will affect your baby.
Ethnicity
In the United States, babies born to black parents are much more likely to have low birth weight than babies of other ethnicities.
However, it is unclear how much of this difference is due to genetics and how much it is a result of the higher poverty rate and associated health problems suffered by some black Americans.
Babies born to parents of all other ethnicities have roughly equal rates of low, medium, and high birth weight.
Maternal age
Younger mothers, those under the age of 20, are more likely to have children of below average weight. Between the ages of 20 and 35, mothers are more likely to have an average-weight baby.
Mothers over the age of 35 tend to have children younger or older than average. About 10% of mothers over 40 have a big baby, compared with 3% of younger mothers.
Maternal health
A mother's pre-existing health conditions, as well as her health during pregnancy, can affect the baby's birth weight.
If a mother has diabetes before becoming pregnant or developing gestational diabetes, she is more likely to have an older baby.
Mothers who have high blood pressure before pregnancy or develop pregnancy-induced hypertension or preeclampsia are more likely to have younger children.
A mother who experiences a lack of healthy nutrition during pregnancy is more likely to have a smaller or larger than average baby.
Smoking tobacco or marijuana during pregnancy is associated with low birth weight. So too is the excessive consumption of alcohol.
Maternal weight gain in pregnancy
How much weight a mother gains during pregnancy, in relation to her starting weight, affects the baby's birth weight.
On average:
Women who eat less than appropriate for their pre-pregnancy weight are more likely to have a smaller than average baby.
Women who take more than the appropriate amount for their pre-pregnancy weight are more likely to have a larger-than-average baby.
Genetics
The birth weight and length of a biological mother and father affect their baby's birth weight. The genetic makeup of the mother and baby and how their respective genetics affect how their bodies interact in the womb also have an impact.
Gestational age
The earlier a baby is born, the less likely it is to weigh more than the average. Unsurprisingly, babies born before 37 weeks are more likely to weigh less than the average. Those born after 40 weeks and 6 days are likely to weigh more than the average.
Birth order
As a rough guide, any baby a mother has with the same biological father will typically be heavier than the last.
However, this is not set in stone - they are proof of that. My second child was born at 40 weeks and weighed 11 pounds 9 and a half ounces, the heaviest of my five babies. Meanwhile, my fourth child was born at 39 weeks and weighed 4 pounds 4 ounces, the lightest of the five.
Are Boy Babies Bigger Than Girls?
All other things being equal, boys tend to weigh slightly more than girls. Some sources pinpoint the extra weight as a few ounces, so it's not a huge difference.
Average Baby Weight By Month
This table shows the average weight of a healthy baby who was born after 37 weeks.
| Age | Boys | Girls |
| 1 Month | 9 lbs 14 oz (4.5 kg) | 9 lbs 4 oz (4.2 kg) |
| 2 Months | 12 lbs 5 oz (5.6 kg) | 11 lbs 4 oz (5.1 kg) |
| 3 Months | 14 lbs (6.4 kg) | 12 lbs 14 oz (5.8 kg) |
| 4 Months | 15 lbs 7 oz (7.0 kg) | 14 lbs 2 oz (6.4 kg) |
| 5 Months | 16 lbs 9 oz (7.5 kg) | 15 lbs 3 oz (6.9 kg) |
| 6 Months | 17 lbs 8 oz (7.9 kg) | 16 lbs 2 oz (7.3 kg) |
| 7 Months | 18 lbs 5 oz (8.3 kg) | 16 lbs 14 oz (7.6 kg) |
| 8 Months | 19 lbs (8.6 kg) | 17 lbs 7 oz (7.9 kg) |
| 9 Months | 19 lbs 10 oz (8.9 kg) | 18 lbs 2 oz (8.2 kg) |
| 10 Months | 20 lbs 3 oz (9.2 kg) | 18 lbs 11 oz (8.5 kg) |
| 11 Months | 20 lbs 12 oz (9.4 kg) | 19 lbs 4 oz (8.7 kg) |
| 12 Months | 21 lbs 3 oz (9.6 kg) | 19 lbs 10 oz (8.9 kg) |
- Between 1 and 3 weeks.
- Between 6 and 8 weeks.
- 3 months.
- 6 months.
- 9 months.
How to Track Average Baby Weight
Keeping an eye on your baby's weight gain or loss is a good thing to do because it can help you spot any problems. Here are some simple ways to control your weight and some tips for doing it correctly.
The best way to track your child's weight is to have them weighed during regular health and development checks. Having the same person weigh your baby on the same equipment makes it easier to compare their weight gains over time. This also allows your doctor to evaluate your baby's weight in the context of his overall health.
Consider buying a baby scale. It is the simplest way to weigh your baby.
If you do not wish to purchase a baby scale, carefully step onto the bathroom scale while holding your baby and then weigh yourself again without your baby. Subtract the lower number from the higher number and this will give you your baby's weight.
A person's weight can vary throughout the day. Instead of weighing your baby every day, do it weekly. This will save you the worry of any small daily fluctuations.
Don't be stressed about any small changes. Instead, mention them to your doctor and observe your baby's overall health. Focus on whether they are okay, feeding as usual, and having wet and dirty nappies.
Keep in mind that all babies are different. Some can gain weight faster than others, and that's okay.
And to avoid going crazy, remember that the exact amount of healthy weight gain for your baby depends on his or her size at birth. That's why medical professionals track baby's weight on graphs that use percentiles.
Understanding the weight percentiles
A percentile chart tracks your baby's weight over time. When your baby is born, his birth weight will be represented on the graph by a dot. This point will be on or near a percentile line.
As your baby grows, his weight will be plotted on the same chart. When you connect the dots that represent your baby's weight, they will form a line. The shape of the curve made by this line is more important than how many pounds or ounces your baby gains.
For example, a baby whose weight is calculated on the 25th percentile at birth is lighter than 75% of other babies. As a child grows, their weight should remain at roughly the same percentile. So at one year, that same baby will still be around the 25th percentile and will be even lighter than the 75th percentile of the other babies.
Likewise, a baby's weight gain reaching the 90th percentile at birth should still be near the 90th percentile at one year.
When the points representing the weights over time are joined together, the shape they create should be roughly the same for both children, even if their weights are different.
All medical professionals use the same percentile growth charts.
If a baby has above or below average weight gain for a few weeks, this is usually not a cause for concern. If your child's weight gain slows down or accelerates noticeably over a longer period of time, this could indicate a health problem.
By drawing a line on a weight chart, it is easy to see if a baby is growing at an average rate. If their growth slows or accelerates over a longer period of time, plotting their growth on a graph will give a differently shaped curve. This allows any medical professional to see, at a glance, whether your baby's weight gain is healthy for them.
Why Is My Baby Not Gaining Weight?
When a child is not gaining the weight they should for a longer period, it is referred to as lack of growth. This is not a disease or a condition in itself. Instead, it is a symptom that a child is not getting the calories they need to gain weight (16).
A child may not gain enough weight if they are not getting enough calories. This could be due to:
Their formula is not mixed properly.
There are difficulties with breastfeeding.
An adult does not recognize a child's hunger cues.
A family cannot afford enough food.
A child may also not gain enough weight because they are not eating enough. This could be due to:
A medical condition such as a cleft palate prevents them from eating enough.
There has been a recent switch to solid foods and the baby has become a picky type.
A developmental delay prevents them from eating enough.
They may also have a failure to gain weight because a medical problem prevents them from using calories. This could happen due to:
Cystic fibrosis, which prevents a person from absorbing calories from food.
Food intolerances such as wheat or dairy products.
Diabetes and other metabolic disorders which allows them to absorb nutrients but prevents the body from using them effectively.
What to do if your baby is not gaining weight
There are practical steps you can take if your baby isn't gaining weight.
The first and foremost thing to do is talk to your doctor. They will help you decide if your child's weight is something that can be monitored or if further investigation is needed.
Participate in all of your child's scheduled development checks. This will ensure that your baby's weight is monitored over the long term.
If your baby is six months old or younger, reduce the amount of solid food you give him. Solid food has fewer calories than the same volume of milk. A baby who fills himself with solid food will not have enough room for the milk he needs.
For younger babies, don't try to breastfeed on a schedule, instead feed him whenever he seems hungry.
If your baby is over six months old, offer healthy foods with a higher calorie count. Bananas, for example, have more calories per ounce than apples.
Make sure your child has a healthy mid-morning and mid-afternoon snack.
What If My Baby Weighs More Than Average?
There is nothing inherently wrong with a child who weighs more than the average. It may be that they are longer than average and their weight is proportional to their length.
This was the case with my eldest son. Although he weighed more than 11 pounds at birth, which is well over the 97th percentile, he was also 24 inches long. That length is still beyond the 97th percentile, so he was a little underweight for his length.
He has grown at an average pace and remains exceptionally large for his age, but in proportion.
There are three main reasons a baby might start gaining more weight than is healthy for him:
Too Many Calories: This could be because foods high in unhealthy fats and sugars are offered, or because their formula is not mixed properly.
Too much food: Even a child who is offered healthy foods can gain weight if he eats more often than necessary or if he snacks too many.
Medical Conditions: Conditions such as hypothyroidism can cause children to gain excess weight, although they typically present with other symptoms such as constipation, poor diet, and noisy breathing.
What to do if your baby is gaining too much weight
There are practical steps you can take if your baby is gaining too much weight.
First, talk to your doctor. Your doctor will be able to tell you if your baby's weight is moving at a healthy pace.
Make sure you mix your baby's formula correctly. Even a little extra dust in the water can lead to excess weight gain if it happens with every meal.
If you are feeding solid foods, be sure to offer healthier foods.
Don't offer too many snacks between meals.
Don't overload your baby with milk and food at night, hoping he will sleep for a longer period. This can result in overeating and the feeling that the sensation is normal.
Weighing Up Your Baby’s Pounds
Healthy babies come in all shapes and sizes. Your child's weight is just one of many indicators of their health.
I'm not going to tell you not to worry about your baby's weight. I know from experience that this is impossible. Instead, I will advise you to try not to obsess over this number and to view your baby's weight in the context of his overall health.
More importantly, if you are unsure, talk to your doctor or other healthcare provider. I am able to consciously discuss your child's weight and advise you if it is something to worry about.
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