Does Where Your Baby Starts on the Growth Chart Affect How They Grow?

What a 2026 study of more than 38,000 children in Europe, the United States and Singapore by Hernandez and colleagues tells families about birth weight percentiles and growth through childhood

A birth weight percentile shows how a baby's weight compares with other babies of the same sex born at the same stage of pregnancy. A large study found that babies born higher within the "normal" range tended to gain weight a little faster as toddlers and were somewhat more likely to be overweight at age 10, while babies born lower showed the opposite. The differences were small for any one child, and regular growth checks remain the best guide.

Almost every parent remembers their baby's birth weight. Fewer are told the number that sits behind it, the percentile, and fewer still are told whether that number matters once the baby goes home. Most babies are simply described as a "normal" size, and the conversation moves on. This article explains what a large international study published in 2026 has learned about whether a baby's exact place on the growth chart at birth is linked to how they grow over the following ten years [1], and what that does and does not mean for families.

What a percentile is, and how doctors have used it

A percentile is a ranking. If a baby is at the 70th percentile for birth weight, it means that out of 100 babies of the same sex born at the same week of pregnancy, about 70 would weigh less and about 30 would weigh more. Doctors compare babies with large reference charts. One widely used international set, called INTERGROWTH-21st, was built from carefully measured newborns of mothers at low risk of growth problems in eight urban areas around the world [2]. For older babies and young children, the World Health Organization (WHO) growth charts are based on healthy, breastfed children studied in six countries [3].

For decades, doctors have sorted newborns into three groups. Babies below the 10th percentile are called "small for gestational age," those above the 90th "large for gestational age," and everyone in between "appropriate for gestational age." Gestational age simply means how many weeks of pregnancy had passed when the baby was born. These labels are useful, but they are statistical cut-offs, not diagnoses: many small babies are simply small and perfectly healthy, many large babies are simply large, and a baby of seemingly normal size can sometimes have had a difficult time growing in the womb [4].

Researchers had long noticed that size and growth in the first months of life are connected to weight later on. A careful review of 24 earlier studies found that babies who were at the heaviest end of the range, or who gained weight especially fast as infants, were more likely to become very overweight (obese) later [5]. Doctors also learned to watch a natural pattern in a child's body mass index, or BMI, a measure that compares weight with height. BMI usually climbs after birth to a high point around 9 months of age [6], drifts down through the toddler years, and then starts to rise again somewhere between 3 and 7 years, a turning point called the "rebound" [7]. A study of more than 51,000 German children found that teenagers with obesity had usually gained weight fastest between ages 2 and 6, and that teenage overweight was more common among children born large (about 44 in 100) than among those born a typical size (about 28 in 100) [8]. Because of findings like these, follow-up advice focused on the two ends of the scale. For babies born small, international experts recommend checking growth in early life and avoiding very rapid weight gain [9]. But a baby at the 15th percentile and a baby at the 85th both counted as "normal," and nobody knew whether their growth paths differed.

How the researchers studied more than 38,000 children

In 2026, Hernandez and colleagues published a study in the journal JAMA Network Open that set out to answer that question [1]. They did not give anyone a treatment. Instead, they used information already collected by seven long-running "birth cohort" studies, which follow large groups of children from pregnancy or birth through childhood, measuring them again and again. Five were in Europe (in Amsterdam in the Netherlands; Bristol and Bradford in England; Nancy and Poitiers in France; and Porto in Portugal), and their 36,018 children, born between 1991 and 2011, formed the main group. These five studies belong to a European network that harmonises data so that researchers can combine cohorts and detect smaller effects [10]. To check whether the results held elsewhere, the team repeated the analysis in 2517 children from a study in Massachusetts in the United States and one in Singapore.

Rather than three groups, the researchers split babies into ten bands by birth weight percentile, from below the 10th up to above the 90th, and compared every band with babies in the middle, between the 40th and 60th percentiles. Using each child's repeated measurements, they worked out how fast children grew in length and weight at 1, 6, 12, and 24 months, how high and how early the BMI peaked in infancy, how high BMI was at the childhood rebound, and whether children were overweight or obese at age 10, using international definitions for children [11]. Almost all of the babies were born at or near full term, on average just under 40 weeks.

What they found

The clearest finding was a smooth, step-by-step pattern. The further above the middle a baby's birth weight percentile was, the faster they tended to gain weight between about 6 months and 2 years, the higher their BMI peaked in infancy, and the higher their BMI was at the rebound. The further below the middle, the opposite was true [1].

The size of these differences is important to keep in perspective. At 2 years of age, babies born above the 90th percentile gained about 40 grams a month more than babies in the middle group, who gained an average of about 543 grams a month. That is roughly 7% more. Babies born below the 10th percentile gained about 29 grams a month less. Differences in length growth were tinier still, a few hundredths of a centimetre a month, and they evened out and even reversed by age 2. In the main group, the timing of the BMI rebound was not clearly linked to birth weight.

At age 10, about 12 in every 100 children in the main group (4307 of 36,018) were overweight or obese. Compared with children from the middle band, those born between the 80th and 90th percentiles had about a 25% higher chance of being overweight, and those above the 90th about a 54% higher chance. Children born between the 10th and 20th percentiles had about a 14% lower chance. In other words, children born in the upper part of the "normal" range, not just those labelled large, showed a somewhat higher risk. The results were similar for boys and girls, similar in the US and Singapore children, and similar when babies born early or late were left out.

Why the familiar labels still matter

This study does not mean that the old three-group system is wrong. When the researchers tested whether using ten bands predicted children's growth better than the usual small, appropriate and large labels, the improvement was modest, and they concluded that the traditional groups remain robust, practical tools [1]. It is also worth knowing that different charts can place the same baby in different bands. When European babies were compared on the international INTERGROWTH-21st chart and on each country's own chart, the international chart labelled far more babies as large in some countries, up to about a quarter of births, and fewer as small [12]. A percentile is a useful guide, not a fixed fact about your child.

What this means for your baby

If your baby was born in the upper half of the normal range, this is not a reason for worry. The study describes patterns across thousands of children; for any one child the differences were small, and overall about 88 in every 100 children were not overweight at 10. Birth weight is only the starting point: an earlier study of nearly 4000 children found that how babies grew after birth, for example whether a large baby's growth gradually settled, was also linked to their weight in early childhood [13]. What the findings do support is paying gentle attention to growth over time. Ask your baby's doctor or nurse what their birth weight percentile was, keep the growth record from routine checks, and talk with them if your child seems to be moving steadily upwards across the lines of the chart. Researchers have argued that this kind of steady upward crossing is a more direct sign of a drift towards extra weight than the timing of the BMI rebound [7].

If your baby was born very early, this study tells us little about them. The children studied were almost all born at or near term, and premature babies have their own growth charts and follow-up, explained in In[Neo]Sight's article on the Fenton growth charts for premature babies.

What researchers are working on next

The children in this study were born 15 to 35 years ago in wealthy countries, so researchers want to know whether the same patterns appear in children born today and in other parts of the world. The study also could not tell whether extra weight was fat or muscle, because BMI does not separate the two. The authors call for tools that combine a baby's birth weight percentile with other early-life information to better predict which children might benefit from extra support, and they suggest that helping babies grow well could start even before birth [1].

For now, the take-home message is a reassuring one. Every baby's growth story begins with their birth weight, but it is not written there. Regular checks, healthy feeding, and an open conversation with your child's care team remain the best ways to support healthy growth.

References

  1. Hernandez MA, Parker RMA, Cole TJ, et al. Birth Weight Percentiles and Infant and Child Growth Dynamics. JAMA Netw Open. 2026;9(7):e2622218. doi:10.1001/jamanetworkopen.2026.22218 ↩
  2. Villar J, Cheikh Ismail L, Victora CG, et al. International standards for newborn weight, length, and head circumference by gestational age and sex: the Newborn Cross-Sectional Study of the INTERGROWTH-21st Project. Lancet. 2014;384(9946):857-868. doi:10.1016/S0140-6736(14)60932-660932-6) ↩
  3. de Onis M, Garza C, Victora CG, Onyango AW, Frongillo EA, Martines J. The WHO Multicentre Growth Reference Study: planning, study design, and methodology. Food Nutr Bull. 2004;25(1 Suppl):S15-26. doi:10.1177/15648265040251S103 ↩
  4. Damhuis SE, Ganzevoort W, Gordijn SJ. Abnormal Fetal Growth: Small for Gestational Age, Fetal Growth Restriction, Large for Gestational Age: Definitions and Epidemiology. Obstet Gynecol Clin North Am. 2021;48(2):267-279. doi:10.1016/j.ogc.2021.02.002 ↩
  5. Baird J, Fisher D, Lucas P, Kleijnen J, Roberts H, Law C. Being big or growing fast: systematic review of size and growth in infancy and later obesity. BMJ. 2005;331(7522):929. doi:10.1136/bmj.38586.411273.E0 ↩
  6. Johnson W, Choh AC, Lee M, Towne B, Czerwinski SA, Demerath EW. Characterization of the infant BMI peak: sex differences, birth year cohort effects, association with concurrent adiposity, and heritability. Am J Hum Biol. 2013;25(3):378-388. doi:10.1002/ajhb.22385 ↩
  7. Cole TJ. Children grow and horses race: is the adiposity rebound a critical period for later obesity? BMC Pediatr. 2004;4:6. doi:10.1186/1471-2431-4-6 ↩
  8. Geserick M, Vogel M, Gausche R, et al. Acceleration of BMI in Early Childhood and Risk of Sustained Obesity. N Engl J Med. 2018;379(14):1303-1312. doi:10.1056/NEJMoa1803527 ↩
  9. Hokken-Koelega ACS, van der Steen M, Boguszewski MCS, et al. International Consensus Guideline on Small for Gestational Age: Etiology and Management From Infancy to Early Adulthood. Endocr Rev. 2023;44(3):539-565. doi:10.1210/endrev/bnad002 ↩
  10. Jaddoe VWV, Felix JF, Andersen AN, et al. The LifeCycle Project-EU Child Cohort Network: a federated analysis infrastructure and harmonized data of more than 250,000 children and parents. Eur J Epidemiol. 2020;35(7):709-724. doi:10.1007/s10654-020-00662-z ↩
  11. Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ. 2000;320(7244):1240-1243. doi:10.1136/bmj.320.7244.1240 ↩
  12. Hocquette A, Durox M, Wood R, et al. International versus national growth charts for identifying small and large-for-gestational age newborns: A population-based study in 15 European countries. Lancet Reg Health Eur. 2021;8:100167. doi:10.1016/j.lanepe.2021.100167 ↩
  13. Taal HR, Vd Heijden AJ, Steegers EA, Hofman A, Jaddoe VW. Small and large size for gestational age at birth, infant growth, and childhood overweight. Obesity (Silver Spring). 2013;21(6):1261-1268. doi:10.1002/oby.20116 ↩