Boys' Growth Glossary
Every term you'll hear at the pediatrician appointment, defined in plain English. Every definition links to a public source you can verify yourself. Thirty terms. Bookmark this before your next visit.
Height percentile
A number 1-99 showing how a child's height compares to peers of the same age and sex. The 50th percentile means half of same-age boys are taller, half are shorter.
For your son: Your son's percentile tells you WHERE he ranks. It does not tell you WHERE he ends up. That's what the growth velocity and mid-parental prediction are for.
Source: CDC growth charts
Growth velocity
Inches or centimeters gained per year. For boys 4-10, normal is 2 to 2.5 inches/year. During puberty peak, it can hit 4 inches/year.
For your son: Growth velocity is a much stronger signal than a single percentile reading. Steady velocity means he's tracking, even if the percentile is low.
Mid-parental height (MPH)
A prediction of a child's adult height using both parents' heights. For boys: (father's height + mother's height + 5 inches) / 2, plus or minus 4 inches for the likely range.
For your son: The single best predictor of your son's adult height that doesn't require any medical test. It's what pediatricians and endocrinologists use.
Constitutional delay of growth and puberty (CDGP)
A pattern where a child is on the low end of normal height AND enters puberty later than peers, but eventually reaches a normal adult height.
For your son: If dad was a late bloomer, your son is likely to be one. CDGP is one of the most common causes of short stature in boys, and it usually requires no treatment.
Familial short stature
Short stature that runs in the family. Both parents are shorter than average, and the child tracks their genetic potential.
For your son: Your son may be short compared to his class but exactly where his family math predicts. If MPH matches his current percentile, familial short stature is the most likely explanation.
Source: American Academy of Pediatrics
Bone age X-ray
An X-ray of the left hand and wrist that shows how mature a child's skeleton is compared to their calendar age. Read against the Greulich and Pyle atlas.
For your son: The single most useful test for a boy who is short and worried. A bone age reading younger than his calendar age means he has more growing time left than peers who look 'on track.'
Source: Stanford Children's Health
Standard deviation score (SDS)
A statistical measure of how many standard deviations a child's height is from the mean for their age and sex. Also called z-score. A height SDS of -2 is roughly the 3rd percentile.
For your son: Endocrinologists prefer SDS to percentile because it's more precise at the tails. If your pediatrician reports an SDS, it's usually a sign they're taking the growth pattern seriously.
Source: WHO Growth Reference
Growth hormone (GH)
A hormone made by the pituitary gland that drives skeletal growth in children. Peaks during sleep, especially deep sleep between 10pm and 2am.
For your son: Growth hormone deficiency is rare (about 1 in 3,500 kids) but real. It's diagnosed with a stimulation test, not from a single blood draw.
Source: NIDDK
IGF-1 (Insulin-like Growth Factor 1)
A hormone made mostly by the liver in response to growth hormone. It's what actually drives cellular growth. Levels can be tested with a blood draw.
For your son: IGF-1 is the most common lab test for suspected growth hormone deficiency. A low IGF-1 doesn't confirm GHD, but a normal one usually rules it out.
Source: StatPearls
Idiopathic short stature (ISS)
Short stature with no identifiable medical cause. Usually defined as height below the 3rd percentile with no growth hormone deficiency, no chronic illness, and no genetic condition.
For your son: ISS is a diagnosis of exclusion. It means the medical workup came back negative and no cause was found. Some children with ISS are candidates for growth hormone therapy.
Source: Endocrine Society, ISS Consensus
Delayed puberty
In boys, no signs of puberty by age 14 (no testicular enlargement, no pubic hair, no voice changes). Most cases turn out to be constitutional delay.
For your son: Delayed puberty is not the same as concerning. Late is usually late, not medically wrong. But past age 14 with no signs is worth a specialist visit.
Tanner stages
Five stages (I-V) that describe physical changes of puberty. Boys typically start Tanner II between ages 9 and 14, peak growth velocity happens in Tanner III to IV.
For your son: Peak growth spurt happens AFTER puberty starts, not before. If your son is 12 and hasn't started puberty yet, his big growth phase is still in front of him.
Source: StatPearls
Testosterone
The main male sex hormone. Rises rapidly during puberty and drives voice changes, body hair, muscle development, and the growth spurt.
For your son: Testosterone doesn't just make him hit puberty, it drives his growth spurt. Boys who enter puberty late have testosterone rising later, and their growth spurt is later too.
Source: Endocrine Society
LH and FSH (Luteinizing hormone, Follicle-stimulating hormone)
Two pituitary hormones that trigger puberty. Low or absent in kids before puberty starts. Rising values in a lab test are the first sign puberty is coming.
For your son: If your pediatrician orders LH and FSH testing on a 14-year-old with no puberty signs, they're looking for hypogonadotropic hypogonadism versus constitutional delay.
Source: StatPearls
Turner syndrome
A chromosomal condition (missing one X) affecting girls, causing short stature and delayed puberty. Occurs in about 1 in 2,500 female births.
For your son: Turner syndrome is female-only. If you have a son, this isn't the diagnosis. But if you have a short daughter, ask about it.
Source: NICHD
Klinefelter syndrome
A chromosomal condition (extra X, XXY) affecting boys. Causes tall stature (not short), delayed puberty, and testicular issues.
For your son: Klinefelter kids are usually TALLER than peers, not shorter. But delayed puberty is the flag.
Source: NICHD
Noonan syndrome
A genetic condition causing short stature, distinctive facial features, and sometimes heart defects. Affects about 1 in 1,000 to 1 in 2,500 births.
For your son: Noonan syndrome is usually diagnosed based on physical features, not height alone. Your pediatrician would already have flagged it.
Source: NIH
Silver-Russell syndrome
A rare genetic condition causing severe growth restriction starting in utero. Affected children are small at birth and remain small.
For your son: Silver-Russell is diagnosed early (usually by age 2). If your son was normal size at birth and grew normally as a toddler, this isn't the diagnosis.
Source: NIH GARD
Peak growth velocity (PHV)
The single fastest year of growth during puberty. Boys typically hit PHV between ages 13-14, gaining 3.5 to 4 inches in that year.
For your son: The peak growth year is often unmistakable. If dad remembers a summer where nothing fit, that was PHV. Late bloomers hit theirs later, but they still hit it.
CDC growth charts
Standard US growth charts published by the CDC in 2000, based on measurements of over 2,000 healthy children. Show percentiles from 3rd to 97th for height, weight, and BMI.
For your son: The CDC charts are what your pediatrician plots your son's height against. They're US-specific and include diverse ethnicities. Not perfect but the standard reference.
Source: CDC
WHO growth standards
International growth standards published by the World Health Organization in 2006. Used for children 0-5. Based on children raised in optimal conditions.
For your son: The AAP recommends WHO standards for the first 2 years and CDC charts after that. Your pediatrician switches at age 2.
Source: WHO
Small for gestational age (SGA)
Born with a birth weight or length below the 10th percentile for gestational age. Some SGA children never fully catch up.
For your son: About 10% of SGA children remain short into adulthood. If your son was SGA at birth AND is currently short, that's worth mentioning to the pediatrician.
Source: AAP
Growth hormone stimulation test
A blood test where growth hormone release is triggered artificially (usually with clonidine or arginine), then measured. Standard test for suspected GH deficiency.
For your son: This is a several-hour test done in a pediatric endocrinology office, not routine bloodwork. Your pediatrician would refer you first.
Source: MedlinePlus
Karyotype
A lab test that examines chromosome structure. Used to check for chromosomal causes of short stature like Turner or Klinefelter syndrome.
For your son: Karyotyping is usually only done when the pediatrician sees specific physical signs. It's not part of routine growth workup.
Source: MedlinePlus
MRI of the pituitary
An imaging test that looks at the pituitary gland (where growth hormone is made). Used when growth hormone deficiency is suspected.
For your son: Only done after growth hormone deficiency has been confirmed by stimulation testing. Rarely a first-line test.
Source: Johns Hopkins
Celiac panel
A blood test that screens for celiac disease, which can cause growth failure. Includes tests for tissue transglutaminase antibodies (tTG-IgA).
For your son: Celiac is a treatable cause of unexplained short stature. A pediatrician doing a proper workup will order this even if there are no gut symptoms.
Source: Celiac Disease Foundation
TSH and Free T4
Blood tests for thyroid function. Both hypothyroidism and untreated hyperthyroidism can affect growth.
For your son: Thyroid testing is standard in a growth workup because it's easy to do and treatable. Ask for TSH and Free T4 if not already done.
Source: American Thyroid Association
Cortisol
The main stress hormone. High cortisol from any cause (Cushing syndrome, long-term steroid use) can slow growth significantly.
For your son: If your son has been on long-term inhaled or oral corticosteroids for asthma, that could be affecting his growth. Worth flagging.
Source: Endocrine Society
Precocious puberty
Puberty starting too early: before age 9 in boys, before age 8 in girls. Early puberty can cause a short adult height because growth stops early.
For your son: Early puberty is the opposite of the late-bloomer question. It's rare in boys but real. If your son has visible puberty signs before age 9, ask about it.
Source: NICHD
Genetic potential
The adult height a child would reach given their parents' heights and no growth-limiting factors. Estimated using the mid-parental height formula.
For your son: Your son's genetic potential is what MPH calculates. If he's tracking well below it, something else is going on. If he's tracking with it, he's on plan.
Source: AAP
Get his numbers in one place
Run the free Growth Check to see his current percentile and where family-height math predicts he lands.
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