What is the Mid-Parental Height (MPH) plus 2 standard deviations (2SD) for this child?

Mid-Parental Height Plus 2 Standard Deviations Calculation

The mid-parental height (MPH) plus 2 standard deviations (2SD) represents the upper limit of a child's expected adult height range based on parental heights, calculated using the formula: MPH + 13 cm + 2SD (8-10 cm) for boys, or MPH - 13 cm + 2SD (8-10 cm) for girls.

Calculating Mid-Parental Height (MPH)

According to current guidelines, mid-parental height is calculated using Tanner's formula 1:

For boys:

MPH = (Father's height + Mother's height + 13) ÷ 2

For girls:

MPH = (Father's height + Mother's height - 13) ÷ 2

Alternatively, the Molinari formula can be used 1:

For boys:

MPH = (Father's height + Mother's height + 10) ÷ 2

For girls:

MPH = (Father's height + Mother's height - 26) ÷ 2

Adding 2 Standard Deviations

After calculating the MPH, add 2 standard deviations to determine the upper limit of the expected height range:

• The standard deviation for adult height is typically 8-10 cm 1
• Therefore, MPH + 2SD equals approximately MPH + 16-20 cm

Clinical Significance

• MPH + 2SD represents the 97th percentile of the expected adult height range based on parental heights 1
• Heights above this threshold may warrant evaluation for conditions causing excessive growth, such as:
  • Growth hormone excess
  • Pituitary gigantism
  • Other endocrine disorders

Example Calculation

For a boy with father's height of 178 cm and mother's height of 165 cm:

1. Calculate MPH using Tanner's formula:

   MPH = (178 + 165 + 13) ÷ 2 = 178 cm

2. Add 2SD (assuming SD = 8 cm):

   MPH + 2SD = 178 + (2 × 8) = 178 + 16 = 194 cm

Therefore, MPH + 2SD for this boy would be 194 cm.

Practical Applications

• Screening for growth disorders: Children with heights exceeding MPH + 2SD should be evaluated for growth hormone excess 1
• Definition of pituitary gigantism: One definition includes height >2 SDS above the mid-parental height 1
• Growth monitoring: Regular plotting of height on appropriate growth charts and comparison to MPH + 2SD helps identify abnormal growth patterns early 2

Important Considerations

• The calculation assumes parents do not have chronic diseases affecting their growth 1
• Different ethnic populations may have different standard deviations for height
• The z-score (SDS) calculation can provide more precise evaluation when needed 1
• For children with suspected growth disorders, bone age assessment of the left wrist is recommended to evaluate growth potential 1

Remember that while MPH + 2SD provides a statistical upper boundary for expected height, individual genetic factors and environmental conditions can influence actual adult height attainment.