Know your baby's gestational age
Fenton charts use post-menstrual age, not chronological age. If your baby was born at 28 weeks and is now 4 weeks old, their gestational age is 32 weeks. This is the number that matters for Fenton chart plotting.
GUIDE
Fenton Growth Charts vs. WHO Growth Charts
Fenton growth charts are specifically designed for premature babies born before 37 weeks, using gestational age to track growth. WHO charts are built for healthy full-term infants. Using the wrong chart for your preemie can lead to inaccurate growth assessments and unnecessary worry.
If your baby was born early, the growth chart matters even more. Fenton charts exist because preemies grow differently — and they deserve a chart that reflects that.
Track preemie growth on Fenton charts
The only baby tracker app with Fenton charts
“The majority of preterm babies catch up with growth and development, especially with early intervention. Early intervention and monitoring is key to successful progress.”
Liz Smith, APRN-NP, Neonatal Nurse Practitioner, Lurie Children's HospitalWhy Preemies Need Their Own Growth Chart
A baby born at 28 weeks gestation is not the same as a baby born at 40 weeks. This seems obvious, but many baby tracking apps and even some pediatric practices plot premature babies on the same WHO charts designed for full-term infants. The result is predictable and harmful: preemie parents see their baby at the 1st or 2nd percentile, panic sets in, and the growth conversation becomes about catching up to a standard that was never designed for them.
Fenton growth charts, developed by Dr. Tanis Fenton and updated in 2013, solve this problem. They were built from a meta-analysis of nearly 4 million preterm birth records from developed countries. The charts track weight, length, and head circumference from 22 weeks gestation through 50 weeks post-menstrual age, using gestational age rather than birth age as the reference point.
This means a baby born at 30 weeks who is now 34 weeks gestational age gets compared to other babies at 34 weeks — not to full-term newborns who had 6 more weeks of in-utero growth. The percentile you see reflects how your preemie is growing relative to babies at the same developmental stage, which is the only comparison that makes clinical sense. Understanding adjusted age vs. actual age is equally important for interpreting these charts correctly.
Fenton vs. WHO Growth Charts
| Aspect | Fenton Growth Charts | WHO Growth Charts |
|---|---|---|
| Designed for | Premature babies born before 37 weeks gestation | Healthy full-term breastfed babies |
| Age tracking | Gestational age (post-menstrual age) | Chronological age from birth |
| Coverage range | 22 weeks gestation to 50 weeks post-menstrual age | Birth (full-term) to 5 years |
| Data source | Meta-analysis of 4 million preterm birth records from developed countries | Healthy breastfed babies from 6 countries (Brazil, Ghana, India, Norway, Oman, US) |
| NICU use | Standard in NICUs worldwide for preterm growth monitoring | Not appropriate for NICU preterm monitoring |
| Catch-up growth tracking | Shows expected preemie growth trajectory, including catch-up periods | Does not account for preemie catch-up growth patterns |
| App availability | Tinylog is the only baby tracker app offering Fenton charts | Available in most baby tracker apps and pediatric offices |
Designed for
Fenton Growth ChartsPremature babies born before 37 weeks gestation
WHO Growth ChartsHealthy full-term breastfed babies
Age tracking
Fenton Growth ChartsGestational age (post-menstrual age)
WHO Growth ChartsChronological age from birth
Coverage range
Fenton Growth Charts22 weeks gestation to 50 weeks post-menstrual age
WHO Growth ChartsBirth (full-term) to 5 years
Data source
Fenton Growth ChartsMeta-analysis of 4 million preterm birth records from developed countries
WHO Growth ChartsHealthy breastfed babies from 6 countries (Brazil, Ghana, India, Norway, Oman, US)
NICU use
Fenton Growth ChartsStandard in NICUs worldwide for preterm growth monitoring
WHO Growth ChartsNot appropriate for NICU preterm monitoring
Catch-up growth tracking
Fenton Growth ChartsShows expected preemie growth trajectory, including catch-up periods
WHO Growth ChartsDoes not account for preemie catch-up growth patterns
App availability
Fenton Growth ChartsTinylog is the only baby tracker app offering Fenton charts
WHO Growth ChartsAvailable in most baby tracker apps and pediatric offices
Fenton charts (2013 revision) are the standard for preterm growth monitoring. WHO charts (2006) are the standard for full-term infants.
Fenton Chart Advantages
- Specifically designed for the unique growth patterns of premature babies
- Uses gestational age — gives accurate percentiles for preemies
- Covers the critical NICU period from 22 weeks gestation onward
- Aligns with WHO charts at 50 weeks, enabling a smooth transition
- Recognized as the global standard for preterm growth assessment in NICUs
Fenton charts are the only clinically appropriate option for monitoring preterm growth before term-equivalent age.
Fenton Chart Limitations
- Limited age range — only covers through 50 weeks post-menstrual age
- Not widely available in consumer baby tracking apps (except Tinylog)
- Based on preterm populations in developed countries — may not represent all preemies
- Parents need to understand gestational age vs. chronological age to interpret correctly
The limited app availability is a significant gap — Tinylog is currently the only baby tracker app offering Fenton charts.
WHO Chart Advantages
- Covers a wide age range — birth through 5 years
- Based on optimal growth conditions — a prescriptive standard
- Recommended by AAP for all full-term babies 0-2 years
- Widely available in pediatric offices and baby tracker apps
- Appropriate for preemies once they reach term-equivalent age and beyond
WHO charts become appropriate once your preemie reaches term-equivalent age.
WHO Chart Limitations for Preemies
- Not designed for premature babies — will give inaccurate percentiles before term age
- Makes preemies appear much smaller than they actually are relative to gestational peers
- Does not account for gestational age — only chronological age
- Can cause unnecessary alarm for preemie parents when their baby 'plots low'
Using WHO charts for preemies before term age gives clinically meaningless percentiles.
The only baby tracker app with Fenton charts.
Tinylog is the only baby tracking app that offers Fenton growth charts for premature babies. Plot your preemie's weight, length, and head circumference on charts designed for their gestational age — not full-term standards that don't apply.
When to Use Each Chart
The answer is straightforward: use Fenton charts from birth through the NICU stay and early post-discharge period for any baby born before 37 weeks gestation. Switch to WHO charts when your preemie reaches term-equivalent age (around 40 weeks post-menstrual age) or when your pediatrician indicates the transition is appropriate — typically by 50 weeks post-menstrual age when the Fenton and WHO curves align.
After the switch, continue using corrected (adjusted) age for WHO chart plotting until your pediatrician says otherwise — usually until age 2-3 for very preterm babies. This means plotting your baby's measurements at their corrected age, not their chronological age, to account for the weeks of growth they missed in utero. Our preemie feeding chart can help you make sure nutrition supports the growth trajectory you're tracking.
The Fenton charts are designed to make this transition seamless. The 2013 revision specifically aligned the Fenton curves with WHO standards at 50 weeks, so there shouldn't be a jarring percentile jump when you switch. For context on how the WHO charts compare to the other common option, see our guide on WHO vs. CDC growth charts. If your baby is at the 40th percentile on Fenton at 50 weeks, they should land near the 40th on WHO charts too.
Tips That Apply Either Way
Expect the Fenton-to-WHO transition
Fenton charts are designed to connect with WHO charts at 50 weeks post-menstrual age. When your NICU team transitions your baby's growth tracking to WHO charts, the percentiles should align smoothly. Ask your pediatrician about the timing of this switch.
Track at home between NICU visits
Preemie parents often feel helpless between NICU visits. Tracking weight, length, and head circumference on Fenton charts at home gives you visibility into your baby's progress and better questions for your care team.
Related Guides
- Baby Growth Percentiles — What percentiles mean and how to interpret them
- Preemie Feeding Chart — Feeding guidelines for premature babies
- Preemie Care Readiness Checklist — Preparing for your preemie's homecoming
Sources
- Fenton, T. R., & Kim, J. H. (2013). "A systematic review and meta-analysis to revise the Fenton growth chart for preterm infants." BMC Pediatrics, 13, 59.
- WHO Multicentre Growth Reference Study Group. (2006). "WHO Child Growth Standards." Acta Paediatrica, 95(S450).
- Fenton, T. R., et al. (2017). "Validating the weight gain of preterm infants between the reference growth curve of the fetus and the term infant." BMC Pediatrics, 17, 38.
- American Academy of Pediatrics Committee on Nutrition. (2014). "Nutritional needs of the preterm infant." Pediatric Nutrition, 8th ed.
- Villar, J., et al. (2015). "Postnatal growth standards for preterm infants: the Preterm Postnatal Follow-up Study." The Lancet, 385(9971).
This guide is for informational purposes only and is not a substitute for professional medical advice. Consult your pediatrician or neonatologist for guidance specific to your premature baby.
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The only baby tracker app with Fenton charts.
Download Tinylog — track your preemie's growth on Fenton charts designed specifically for premature babies.