Researchers from the Perinatal Institute found that non-customised fetal growth charts used across the NHS often misclassify babies, potentially increasing the risk of avoidable stillbirths. A study published in The BMJ suggests that using customised GROW charts, which adjust for maternal weight and ethnicity, provides more accurate data for monitoring pregnancy safety.
Why do current fetal growth charts risk misclassifying babies?
Standard “one-size-fits-all” growth charts can incorrectly identify babies as being either too small or too large for their gestational age. According to a study published in The BMJ, these misclassifications can lead to missed cases of fetal growth restriction (FGR) or, conversely, lead to unnecessary medical interventions.
Fetal growth restriction occurs when a baby’s growth in the womb is slower than expected. The Perinatal Institute notes that the lack of recognition of FGR during pregnancy is the most frequent cause of avoidable stillbirth. Because of this, researchers argue that accurate measurement is a fundamental requirement for the safety of both mother and baby.
How do the different NHS growth charts compare?
Various fetal weight charts are currently used across NHS hospitals to define small and large for gestational age babies. These include the Hadlock, Intergrowth-21st (IG21), World Health Organisation (WHO), and Fetal Medicine Foundation (FMF) charts. Most of these are unadjustable, meaning they do not account for individual maternal characteristics.
The study highlighted significant discrepancies in how these charts identify small for gestational age (SGA) babies at term (37+ weeks). When comparing the rates of babies identified as being below the 10th centile, the data showed:
- Intergrowth-21st: 4.8%
- GROW (customised): 12.3%
- WHO and FMF: 17.2%
The researchers found that because “universal” charts are often derived from populations in other countries, the rates of babies identified as too small or too large varied widely between different local Integrated Care Boards (ICBs) due to local population differences.
What did the Perinatal Institute study reveal?
Researchers at the Perinatal Institute in Birmingham analysed 3.2 million births between 2015 and 2025. The study encompassed 38 of the 42 NHS integrated care boards (ICBs) in England.
The findings indicate that customised GROW charts—which adjust for a mother’s weight and ethnic origin—provide more accurate and consistent data. While unadjustable charts showed wide variation across different regions, the GROW standard remained consistent because it adjusts for the normal variations found in the UK population.
Research limitations
The authors acknowledged that these are observational findings. They also noted that the study used birthweight rather than ultrasound-estimated weight to assess how the charts performed. However, they stated this method allowed all cases to be included, regardless of whether the mother had received growth scans during pregnancy.
What is the future of NHS maternity care standards?
The authors of the study are calling for the urgent standardisation of growth charts used across the NHS. A recent BMJ Analysis by the Perinatal Institute highlighted a critical need for the NHS to improve the prevention of avoidable perinatal deaths.
The research suggests that individual NHS trusts often deal with rare but catastrophic outcomes that may result from local protocols and practices being implemented too late. To move toward a safer maternity model, researchers propose two major shifts:
- Co-ordinated Programming: A coherent programme across the entire NHS to ensure consistency in growth assessment.
- National Oversight: The establishment of real-time national oversight to monitor quality and safety in maternity care.
Frequently Asked Questions
What is fetal growth restriction (FGR)?
FGR is a condition where a baby’s growth in the womb is slower than expected, which can increase the risk of adverse pregnancy outcomes.
Why do customised growth charts like GROW exist?
Customised charts adjust for maternal characteristics, such as weight and ethnic origin, to provide a more accurate assessment of a baby’s growth relative to the mother.
Why are there different growth charts in the NHS?
Different hospitals use various charts, such as WHO or FMF, which were often developed using data from different international populations and may not reflect local demographics.
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