The Little Chart on the Wall: How Doctors Track Your Premature Baby's Growth — and How That Chart Just Got a Major Upgrade

From a handwritten grid in 1948 to a study of 89,218 babies: the long story of how scientists learned what premature growth really looks like

Why Your Baby's Weight Is Plotted on a Chart Every Day

If your baby was born premature and is in a neonatal intensive care unit (NICU), you have almost certainly seen the nurses weigh your baby every morning. That weight gets plotted on a chart — sometimes on paper, sometimes on a screen — that shows whether your baby is growing as expected.

Those charts matter enormously. They shape whether doctors adjust your baby's feeds, whether a nutrition specialist is called, and how the care team talks about whether your baby is thriving. For parents, watching a dot move up or down can feel like watching a report card every single day.

Here is something that may surprise you: the charts themselves have a history, and that history is not simple. For decades, the charts used to monitor premature babies' growth were based on estimates of how babies grow inside the womb — not on data about what premature babies actually do after birth [1]. A major study published in 2023 has now shown, more definitively than ever before, that those two things are very different [1]. Understanding this history can help you make sense of conversations with your care team.

1948: The First Chart Is Drawn

The story begins in 1948, when a doctor named Joseph Dancis and colleagues O'Connell and Holt published a small but pioneering paper [2]. There was no standard way for nurses and doctors to record and track premature babies' weight, so the team watched about 100 babies born weighing roughly 1,000 to 2,500 grams — about 2 to 5.5 pounds — who had fairly smooth hospital stays. They plotted how weight changed over time and grouped the curves by birth weight. The result was a simple grid: a chart that any nurse or doctor could use to mark a baby's daily weight and compare it against other premature babies of similar size.

This filled a real gap. The problem was what happened next: the Dancis chart stayed in use for more than 50 years [3]. By the 1990s, premature babies were surviving at birth weights and gestational ages unimaginable in 1948, intensive care had transformed the NICU, and feeding practices had changed enormously. Yet the chart on many neonatal unit walls was still the one Dancis had drawn from babies cared for under 1940s conditions.

1999: The First Big Modern Study

In 1999, a large team led by Dr Richard Ehrenkranz at Yale University published a new growth study far more rigorous than anything that had come before [4]. It enrolled 1,660 premature babies — those born weighing between 501 grams (just over a pound) and 1,500 grams (about 3.3 pounds) — across 12 hospitals in the United States between 1994 and 1995.

The team measured weight every day during the early weeks of life, and measured length, head circumference, and arm circumference every week. It produced growth curves that reflected what premature babies actually do — including the initial weight loss that all premature babies experience before they start gaining again.

A follow-up study in 2006 [5] looked at the tiniest babies — those born under about 2.2 pounds — and found that babies who grew more quickly during their NICU stay had better brain development outcomes at 18 to 22 months. The fastest-growing group were less likely to have cerebral palsy and more likely to score in the normal range on developmental tests. This became one of the key reasons doctors and nurses are so focused on helping premature babies grow well during their hospital stay.

2015: A Global Standard From Eight Countries

By 2015, researchers were asking a different question. The Ehrenkranz study had described what premature babies in 1990s US hospitals actually grew like. But what about premature babies born in the best possible circumstances — where mothers were well-nourished, healthcare was excellent, and babies were breastfed in optimal conditions around the world?

The INTERGROWTH-21st Project, led by researchers at the University of Oxford, studied pregnant women in eight cities across Brazil, China, India, Italy, Kenya, Oman, the United Kingdom, and the United States [6]. Among more than 4,600 women enrolled, 224 premature babies were born. Of those, 201 (90%) were followed closely after birth.

The team's charts showed that charts based on what fetuses weigh at different gestational ages were not the right tool for tracking growth after birth [7]. After birth, premature babies follow their own path, distinct from how fetuses grow in the womb. The INTERGROWTH-21st charts cover this postnatal path up to around 64 weeks of postmenstrual age — roughly 6 months after the original due date — at which point standard WHO infant growth charts become appropriate.

2023: The Largest Study Ever — and a Surprising Finding

In 2023, Dr Fu-Sheng Chou, Dr Hung-Wen Yeh, and Dr Reese Clark published a landmark study in the journal Nature Communications [1]. It drew on data from 89,218 very premature babies — those born before 32 weeks of pregnancy — who were cared for in Pediatrix Medical Group NICUs across the United States between 2010 and 2020. This is one of the largest datasets of premature infant growth ever assembled, representing nearly 5.5 million individual weight measurements, over 750,000 length measurements, and over 1.3 million head circumference measurements.

The team used this enormous dataset to build detailed growth charts — the 2023 Postnatal Growth Charts for Preterm Infants — that are specific to each sex and gestational age group. Then they asked a key question: how did the growth of these real babies compare to the standard widely used in NICUs, the Fenton chart [11], which is based on estimates of how babies grow inside the womb — the growth target recommended by the American Academy of Pediatrics [9]?

The answer was striking. When the actual measurements of these 89,218 babies were plotted on the Fenton womb-growth chart, 70 to 90 percent of the measurements fell below the 50th percentile line — the middle of the chart — and 25 to 50 percent fell below the 10th percentile line, which is usually considered a sign of poor growth.

Does that mean all of these babies were growing badly? No. It means the chart was calibrated to the wrong reference. These babies were following their own biological path — the path of premature babies growing outside the womb — which is structurally different from the path of a baby growing inside the womb.

What "Structurally Different" Actually Means

The 2023 study did not just find a general difference — it identified three specific features of premature postnatal growth that do not exist in fetal growth:

The initial dip. Very premature babies lose weight in the first days after birth. This is entirely normal — it reflects the adjustments a tiny baby's body makes to being outside the womb, including changes in fluid balance. In the Chou study, the lowest weight point was typically around day 4 of life, and babies generally regained their birth weight by days 8 to 10. This pattern does not exist in fetal growth, because babies inside the womb do not lose weight and then gain it back.

No third-trimester slowdown. Fetal growth naturally slows down in the last weeks of pregnancy before birth. After birth, very premature babies do not show this slowdown. Their growth rate continues to accelerate, which is actually a sign that their biology is responding appropriately to the world outside the womb.

A slow-then-fast pattern in length and head size. For length and head circumference, premature babies initially grow slowly after birth and then speed up — the opposite of what happens in the womb. This means that in the early weeks, a premature baby's length and head circumference may look like they are lagging when compared to fetal standards, but they are actually following a normal postnatal pattern.

What This Means for Your Baby's Care

If your baby is being monitored with the 2023 postnatal growth charts, or if your care team uses them alongside other tools, the numbers have a more accurate foundation.

Interpreting the early weight loss. When you see your baby's weight drop in the first few days, this is not a sign that something is going wrong. The Chou study confirmed that the initial dip — reaching its lowest around day 4 and recovering by days 8 to 10 — is a normal feature of premature postnatal physiology [1].

Understanding why growth matters. The Ehrenkranz 2006 follow-up showed that babies who grow faster in the NICU tend to do better on developmental tests at 18 to 22 months [5]. This is why your team puts so much focus on nutrition — the goal is not just a number on the scale, but supporting your baby's brain and body development.

Growth charts are tools, not report cards. No chart tells the whole story. Charts help doctors spot patterns that need attention, but they are always interpreted alongside illness, feeding tolerance, blood results, and dozens of other pieces of information. A single point below a percentile line is one data point in a much larger picture.

The Road Ahead

The 2023 study answered a question debated for decades: can premature babies, even with the best modern nutrition, grow at the same rate as babies inside the womb? The answer is no — and this is not a failure of modern care. It reflects something fundamental about what it means to be born very early. The biology of premature postnatal growth is different from fetal biology, and the tools used to monitor it should reflect that reality [1].

Researchers are now working to understand how growth trajectories on the new postnatal charts relate to long-term outcomes like brain development, vision, and lung health [8]. Future work will also address how to best assess growth in these infants — including which measurements matter most and how to interpret them [10] — and how these charts should connect to the growth monitoring tools used after a baby goes home.

For now, the most important thing to know is that the NICU team watching your baby's weight every morning is using the best available science to interpret what they see. And that science has just taken a significant step forward.

References

  1. Chou FS, Yeh HW, Clark RH. A comparative study of postnatal anthropometric growth in very preterm infants and intrauterine growth. Nat Commun. 2023;14:5626. doi:10.1038/s41467-023-41069-0 ↩
  2. Dancis J, O'Connell JR, Holt LE Jr. A grid for recording the weight of premature infants. J Pediatr. 1948;33:570–572. ↩
  3. Blond MH, Gold F, al Kadiry L, Rondeau C, Marchand S, Guérois M. Post-natal weight gain in the premature: the reference curves of Dancis (1948) can still be used. Arch Pediatr. 1994;1(12):1079–1084. doi:10.1016/S0929-693X(05)80451-380451-3) ↩
  4. Ehrenkranz RA, Younes N, Lemons JA, Fanaroff AA, Donovan EF, Wright LL, Katsikiotis V, Tyson JE, Oh W, Shankaran S, Bauer CR, Korones SB, Stoll BJ, Stevenson DK, Papile LA. Longitudinal growth of hospitalized very low birth weight infants. Pediatrics. 1999;104(2 Pt 1):280–289. doi:10.1542/peds.104.2.280 ↩
  5. Ehrenkranz RA, Dusick AM, Vohr BR, Wright LL, Wrage LA, Poole WK. Growth in the neonatal intensive care unit influences neurodevelopmental and growth outcomes of extremely low birth weight infants. Pediatrics. 2006;117(4):1253–1261. doi:10.1542/peds.2005-1368 ↩
  6. Villar J, Giuliani F, Bhutta ZA, et al; INTERGROWTH-21st. Postnatal growth standards for preterm infants: the Preterm Postnatal Follow-up Study of the INTERGROWTH-21st Project. Lancet Glob Health. 2015;3(11):e681–e691. doi:10.1016/S2214-109X(15)00163-100163-1) ↩
  7. 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) ↩
  8. Fenton TR, Kim JH. A systematic review and meta-analysis to revise the Fenton growth chart for preterm infants. BMC Pediatr. 2013;13:59. doi:10.1186/1471-2431-13-59 ↩
  9. American Academy of Pediatrics, Committee on Nutrition. Nutritional needs of low-birth-weight infants. Pediatrics. 1977;60:519–530. doi:10.1542/peds.60.4.519 ↩
  10. Horbar JD, Ehrenkranz RA, Badger GJ, et al. Weight growth velocity and postnatal growth failure in infants 501 to 1500 grams: 2000–2013. Pediatrics. 2015;136(1):e84–e92. doi:10.1542/peds.2015-0129 ↩
  11. Clark RH, Olsen IE, Spitzer AR. Assessment of neonatal growth in prematurely born infants. Clin Perinatol. 2014;41:295–307. doi:10.1016/j.clp.2014.01.017 ↩