The new growth charts were constructed with 9 centiles (99.6th, 98th, 91st, 75th, 50th, 25th, 9th, 2nd and 0.4th). The 9 centiles are spaced two-thirds (0.67) of a standard deviation (SD) apart. The two extreme centile lines (0.4th and 99.6th) may help screen out the more likely abnormal growth for further evaluation.
There was an increase of about 2cm in median height at 18 years in boys (170.9cm in 1993 to 172.5cm in 2020) and girls (158.2cm in 1993 to 160.2cm in 2020).
To avoid normalising childhood obesity, HK2020 weight-for-age charts were constructed using actual weight in 0-2.0 years and derived weight in >2-18 years.
Since the measurements at birth contributing to the HK2020 Growth References were from contemporary healthy term newborns of Hong Kong, with the majority born just under 39 weeks, birth weight centiles of HK2020 at age 0 represents birth weight of babies born at 38-39 weeks. As such a transition from preterm gestation-specific birth weight charts to HK2020 at 38-39 weeks may provide a smoother transition than 40 weeks.
There is a “structural” step of 7mm at 2 years when the measurement changes from supine length to standing height.
An auxiliary growth assessment tool, mid-parental height comparator was created for healthcare professionals’ use. Majority of children’s height centiles are within two centile spaces above or below the mid-parental centile. Comparison with parents’ height should not be seen as a test for normal height and a child growing abnormally may still be within the parental height range.
The HK2020 Growth References do not include weight-for-length/height charts because body shape related to height varies by age in young children, making the ratio of weight to length/height an unsatisfactory marker of obesity. Childhood obesity will be defined by BMI-for-age instead of weight-for-length/height.
The HK2020 Growth References do not include pubertal development charts.
The data collection period (November 2019 to October 2022) coincided with the COVID-19 pandemic, resulting in concerns of the impact of home confinement and school closure on changes in diet, lifestyle and growth of children. However children taking part in the Hong Kong Growth Survey 2020-22 were not fatter (as indicated by BMI) compared to toddlers attending MCHC and students attending SHS in recent years. BMI and weight data above 2 years collected from HK growth survey were not used in the construction of new growth references and thus the impact of the pandemic on BMI-for-age reference is likely minimal.