Supplementation and nutritional interventions that pregnant mothers take can affect a wide range of outcomes for their children after they’re born, including the child’s body mass index (BMI).
While BMI for adults is calculated by adjusting the adult’s weight based on their height, BMI for children is more complicated, since a child’s height is changing rapidly as they grow. To account for this, charts have been developed based on age and sex to see how far away from average any given girl or boy is at a certain age.[1][2] These can be expressed as either percentiles or z-scores. A z-score is a standardized way to state how far away from the mean a measurement is. If the z-score is 0, it means that the value in question is identical to the mean value for the group. A positive or negative z-score reveals how many standard deviations away from the mean a measurement is, with positive values meaning that the measurement in question is above the mean, while negative values would be below it.
Just like with adults, “overweight” and “obese” can be defined using age-based BMIs for children. Overweight for a child is defined as a BMI-for-age equal to or greater than the 85th percentile and less than the 95th percentile. Obesity for a child is defined as a BMI-for-age equal to or greater than the 95th percentile.[3] And just like with adults, these age-based BMIs for children can serve as a proxy for amount of body fat, albeit a far from perfect one.[4]
