growth chart was subsequently used by the World Health Organization for dissemination to healthcare systems abroad. In order to accommodate for heterogenous populations internationally, the WHO made an effort to gather data from different regions in every continent. Data used to calculate the CDC's growth chart percentiles was accumulated periodically since the 1960s by the National Health and Nutrition Examination Survey. Updated and more comprehensive data was later used to revise the existing growth chart and construct the 2000 CDC growth charts. The revised growth charts include revision of the 14 existing charts as well as introduction of 2 new BMI-for-age charts. Quantitative Definitions Mid-parental height (MPH) is a quantity used to predict the target height of an individual based on the heights of the two biological parents. It can be used to calculate the target height (TH) for children assigned male (AMAB) or female (AFAB) at birth. MPH = TH for AFAB = TH for AMAB = Velocity is another quantity that is used to quantify growth curves. It can be used for both height and weight. In the equation provided q is either weight or height, t represents time, and Δ represents change over a defined interval. Growth velocity is defined as follows. Body mass index (BMI) is a useful quantification that can gauge level of obesity. It is defined as follows with the given clinical ranges. Obesity: BMI > 95th percentile Overweight: 85th < BMI < 95th percentile Underweight: BMI < 5th percentile Bone age is another useful metric that complements a physician's use of a growth chart. It is particularly useful in working up growth abnormalities and can indicate a delay in onset of puberty. Common Variants of Normal Growth Familial short statue: Benign variant of normal height growth. Expect a normal bone age and a trajectory that is on track for the target height. Constitutional growth delay: Benign variant of normal height growth due to a delay in the onset of puberty. Expect a delayed bone age and a trajectory that is not on track for the target height. Endocrine Disorders: Pathologic variant of normal growth due to hormonal abnormality. Expect a delayed height trajectory accompanied by a gain of weight. Clinical Significance The combination of height and weight velocity can indicate underlying disease of genetic origin, endocrine cause, and/or delayed growth. Normal Growth Deficiency One of the most common growth disorders, a growth deficiency