Doctors assess puberty development using a combination of physical examination, growth tracking, blood tests, and sometimes imaging. The cornerstone is a standardized rating system called the Tanner Stages, which scores physical changes on a scale from 1 (no development) to 5 (fully mature). Beyond that visual and physical assessment, doctors may order hormone levels, a bone age X-ray, or an ultrasound depending on whether puberty seems to be arriving too early, too late, or progressing unusually.
The Tanner Stages Physical Exam
The Tanner scale is the primary tool doctors use to gauge where a child is in puberty. It was developed decades ago and remains the clinical standard worldwide. The exam is quick and involves a visual assessment of specific body areas, scored from Stage 1 (prepubertal) through Stage 5 (adult).
For girls, doctors evaluate breast development. Stage 1 means no breast tissue is present. Stage 2, the first true sign of puberty in girls, is a small breast bud felt under the areola. By Stage 3, breast tissue extends beyond the areola. Stage 4 shows the areola rising above the breast contour in a “double scoop” shape. Stage 5 is the mature adult breast with a single smooth contour.
For boys, the key marker is testicular size. Doctors may use a tool called an orchidometer, which is a string of oval beads in graduated sizes held next to the testicle for comparison. A testicular volume of 4 milliliters (or a length of 2.5 centimeters) marks the official onset of puberty in boys. This typically happens around age 11 to 12, though it can occur normally anywhere from about 10 to nearly 14.
In both sexes, pubic hair is scored separately on its own five-stage scale, from no hair (Stage 1) through sparse downy hair (Stage 2) to full adult distribution that extends onto the inner thighs (Stage 5). A child’s pubic hair stage and breast or genital stage don’t always match up perfectly, which is normal.
Growth Tracking and Height Velocity
Height is one of the most accessible clues to pubertal timing. Before puberty, most children grow at a steady 5 to 6 centimeters per year. During the pubertal growth spurt, that rate accelerates noticeably. Girls typically hit their fastest growth around ages 11 to 12, while boys peak later, around 13 to 15. Boys in one large study gained roughly 20 centimeters over the three years leading up to their peak growth rate, averaging about 6.4 centimeters per year during that window.
Doctors plot height measurements on standardized growth charts at each visit. A sudden upward jump on the curve often signals that puberty is underway, even before other signs are obvious. Conversely, a child who stays flat on the growth curve while peers are shooting up may warrant further evaluation for delayed puberty.
Blood Tests for Hormone Levels
When the physical exam raises questions, doctors often draw blood to measure reproductive hormones. The two most important are luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These are produced by the brain’s pituitary gland and act as the “on switch” for puberty, telling the ovaries or testes to start producing sex hormones.
In girls, LH levels rise sharply as puberty begins. The upper limit of the normal LH range roughly triples between the 6-to-10 age group and the 11-to-15 group, jumping from about 5 to over 13 IU/L. FSH rises alongside it, and estradiol (the main estrogen) climbs from undetectable levels to 87 pg/mL or higher by mid-puberty. In boys, testosterone is the key sex steroid, while LH increases are more gradual.
These hormone tests help doctors distinguish between central puberty, which starts in the brain and follows the normal biological pathway, and peripheral causes, where sex hormones are being produced by a tumor or other source without the brain’s signal. If LH is elevated, the brain is driving puberty. If LH is low but sex hormones are high, something else is going on.
Bone Age X-Ray
A bone age assessment is one of the most commonly ordered tests when puberty timing seems off. It involves a single X-ray of the left hand and wrist. The bones in the hand mature in a predictable sequence, and by comparing the X-ray to a reference atlas (the Greulich and Pyle atlas, in most cases), a radiologist assigns a “bone age” that may differ from the child’s actual age.
A child whose bone age is significantly ahead of their chronological age may be experiencing early puberty. Sex hormones accelerate bone maturation, so a 7-year-old girl showing breast development whose bones look like those of a 10-year-old is a clear signal that puberty hormones are active. On the other hand, a child with delayed puberty often has a bone age that lags behind, which can actually be reassuring: it means there’s still growth potential remaining in the bones.
Pelvic Ultrasound for Girls
In some cases, particularly when evaluating early puberty in girls, doctors order a pelvic ultrasound. This painless, external scan measures the size and shape of the uterus and ovaries, both of which change dramatically during puberty.
Before puberty, the uterus is small and tubular, measuring about 2.5 to 4 centimeters long and less than 1 centimeter thick. As puberty progresses, the uterus takes on an adult pear shape. The upper portion (fundus) enlarges disproportionately, and total length reaches 5 to 8 centimeters. The ovaries grow too, expanding from about 1 to 2 centimeters prepubertally to 2 to 4 centimeters in the premenarchal stage. By the time of the first growth spurt, ovarian volume can reach around 8 cubic centimeters as follicles begin maturing.
These measurements help doctors confirm whether the body is truly responding to pubertal hormones or whether physical signs like breast swelling have another explanation, such as excess body fat or a benign cyst.
When Timing Triggers an Evaluation
Not every child needs blood tests or imaging. Most of the time, a doctor tracks Tanner staging and growth curves at routine checkups and everything proceeds normally. Testing becomes important when puberty falls outside the expected window.
Puberty is considered early (precocious) if it starts before age 8 in girls or before age 9 in boys, though Black, Hispanic, and Native American children may naturally begin somewhat earlier. On the other end, doctors evaluate for delayed puberty if a girl shows no breast development by age 12, hasn’t had a first period by age 15, or if more than five years pass between the start of breast growth and menstruation. For boys, the thresholds are no testicular enlargement by age 14 or no pubic hair by age 15.
In these situations, the evaluation typically layers several of the tools described above: a careful Tanner staging exam, hormone blood work, a bone age X-ray, and potentially imaging. Together, these give doctors a detailed picture of whether puberty is simply running on a different schedule or whether an underlying condition needs attention.