SGA, AGA or LGA classification
Classifying birth weight for gestational age identifies the small (SGA), appropriate (AGA) or large (LGA) newborn, which guides the risk of hypoglycemia, hypothermia and polycythemia and the follow-up plan. This calculator uses the Fenton 2025 cut-offs, separated by sex, from 22 to 42 weeks.
Enter sex, gestational age at birth (completed weeks) and birth weight. The calculator compares the weight with the Fenton 2025 3rd, 10th, 90th and 97th percentiles and classifies the newborn as SGA, AGA or LGA.
SGA: weight below the 10th percentile. AGA: between the 10th and 90th percentiles. LGA: above the 90th percentile. Fenton 2025 size-for-GA cut-off table (free download), which covers weight only and at birth only; it does not replace the full Fenton chart for following length, head circumference or trajectory.
Clinical decision-support tool for use by healthcare professionals. It does not replace clinical judgment or your unit's protocols.
Definitions
SGA: weight below the 10th percentile for gestational age and sex. AGA: between the 10th and 90th percentiles. LGA: above the 90th percentile. The calculator also reports whether the weight is below the 3rd or above the 97th percentile, ranges that indicate a more marked deviation.
Source and limits
The cut-offs come from the Fenton 2025 meta-analysis for size-at-birth assignment, a free download from the University of Calgary. They cover weight only and at birth only. Length, head circumference and trajectory follow-up require the full Fenton chart or Intergrowth-21st.
Example
Girl born at 30 weeks weighing 1,150 g. The 30-week cut-offs for females are 1,086 g (p3), 1,194 g (p10), 1,735 g (p90) and 1,882 g (p97). The weight lies between the 3rd and 10th percentiles: SGA. Monitor glucose and temperature and plan growth follow-up with corrected age.
Frequently asked questions
Is SGA the same as intrauterine growth restriction?
No. SGA is a statistical classification by birth weight. Growth restriction is a diagnosis of fetal growth below potential, which can occur in AGA newborns. Every SGA infant should be assessed, but not every SGA infant was growth restricted.
Can I use this calculator to follow growth in the NICU?
No. The cut-offs apply to birth weight. To follow the trajectory of weight, length and head circumference in the NICU, use the full Fenton chart or Intergrowth-21st, plotting by postmenstrual age.
Why are the cut-offs separated by sex?
Boys are on average heavier than girls at the same gestational age. A single curve would classify girls as LGA and boys as SGA more often than is real.
References
- Fenton TR, et al. 2025 meta-analysis for size for gestational age (small, large and appropriate) assignment at birth, V2. University of Calgary; ucalgary.ca/resource/preterm-growth-chart.
- Fenton TR, Kim JH. A systematic review and meta-analysis to revise the Fenton growth chart for preterm infants. BMC Pediatr. 2013;13:59.
- Brazilian Society of Pediatrics (SBP). Follow-up manual for the high-risk newborn. 2nd ed. 2024. Chapter 9.
