An investigator for a nationally representative health survey is evaluating the heights and weights of men and women aged 18–74 years in the United States. The investigator finds that for each sex, the distribution of heights is well-fitted by a normal distribution. The distribution of weight is not normally distributed. Results are shown: Mean Standard deviation Height (inches), men 69 0.1 Height (inches), women 64 0.1 Weight (pounds), men 182 1.0 Weight (pounds), women 154 1.0 Based on these results, which of the following statements is most likely to be correct?

99.7% of heights in women are likely to fall between 63.7 and 64.3 inches.

86% of heights in women are likely to fall between 63.9 and 64.1 inches.

68% of weights in women are likely to fall between 153 and 155 pounds.

95% of heights in men are likely to fall between 68.85 and 69.15 inches.

99.7% of heights in men are likely to fall between 68.8 and 69.2 inches.

A 1-year-old male presents to his pediatrician for a well-child visit. Through a history from the mother and physical examination, the pediatrician learns that the baby babbles non-specifically, takes several steps independently, and picks up his cereal using two fingers. His weight is currently 22 lbs (birth-weight 6 lbs, 9 oz), and his height is 30 inches (birth length 18 inches). Are there any aspects of this child's development that are delayed?

There are no developmental concerns

A 2-month-old is brought to the physician for a well-child examination. She was born at 39 weeks gestation via spontaneous vaginal delivery and is exclusively breastfed. She weighed 3,400 g (7 lb 8 oz) at birth. At the physician's office, she appears well. Her pulse is 136/min, the respirations are 41/min, and the blood pressure is 82/45 mm Hg. She weighs 5,200 g (11 lb 8 oz) and measures 57.5 cm (22.6 in) in length. The remainder of the physical examination is normal. Which of the following developmental milestones has this patient most likely met?

Absence of asymmetric tonic neck reflex

A 4-year-old boy is brought to the pediatrician by his mother for a routine medical examination. His medical history is relevant for delayed gross motor milestones. The mother is concerned about a growth delay because both of his brothers were twice his size at this age. Physical examination reveals a well-groomed and healthy boy with a prominent forehead and short stature, in addition to shortened upper and lower extremities with a normal vertebral column. The patient’s vitals reveal: temperature 36.5°C (97.6°F); pulse 60/min; and respiratory rate 17/min and a normal intelligence quotient (IQ). A mutation in which of the following genes is the most likely cause underlying the patient’s condition?

Fibroblast growth factor receptor 3

Runt-related transcription factor 2

Insulin-like growth factor 1 receptor

An 18-month-old boy is brought to the physician by his mother because of concern that he has not yet begun to walk. He was born at term and exclusively breastfed until 15 months of age. His mother says he has been well, apart from an episode of high fever and seizure 4 months ago for which she did not seek medical attention. He has an older brother who is currently receiving medical treatment for failure to thrive. His parents have no history of serious illness; they are of normal height. His last vaccine was at the age of 4 months. He is at the 20th percentile for length, 10th percentile for weight, and 50th percentile for head circumference. Physical examination shows dry mucous membranes and erosion of the enamel on the lingual surface of the incisors and carious molars. He has frontal bossing. His wrists are widened, his legs seem bent, and there is beading of the ribs. Which of the following is the most likely underlying cause of this patient's delay in walking?

Defective growth plate mineralization

Deficiency of osteoclasts to reabsorb bone

Osteoid proliferation in the subperiosteal bone

Mutation of fibroblast growth factor receptor 3

A 6-month-old girl is brought to the physician because of drooling and excessive crying for 3 days. She calms down when cuddled or with a pacifier in her mouth. She feeds well and has no vomiting or diarrhea. She was breastfed exclusively for 5 months. She is given no medications and was born at 39 weeks gestation via spontaneous vaginal delivery. She is up to date on all vaccines and is meeting all developmental milestones. At the clinic, her weight is 7.3 kg (16 lb 1 oz) and her height is 65.8 cm (25.9 in) in length. She appears irritable. Her pulse is 124/min, the respirations are 32/min, the blood pressure is 92/63 mm Hg, and the temperature is 36.8°C (98.2°F). On physical examination, she has no conjunctivitis, cervical lymphadenopathy, or pharyngeal erythema. Which element of the physical examination is most likely to be present in this patient?

Eruption of mandibular incisors

Crying on frontal sinus palpation

Closure of the anterior fontanel

Erythema and fluctuance of the submandibular area

Normal growth patterns for USMLE Step 2 CK: High-Yield Pediatrics Lessons

Anthropometry - The Measure of a Tot

Weight (Wt):
- Doubles by 5 months, Triples by 1 year, Quadruples by 2 years.
- Daily gain: 25-30 g for first 3 months.
- Wt for age (kg) [2-6 yrs]: $(Age_{yrs} \times 2) + 8$.
Height/Length (Ht):
- At birth: ~50 cm; 1 yr: ~75 cm; 4 yr: ~100 cm (doubles).
Head Circumference (HC):
- At birth: ~35 cm; 1 yr: ~45 cm.
Mid-Upper Arm Circumference (MUAC):
- Relatively constant from 1-5 years.
- Normal: >13.5 cm; SAM: <11.5 cm.

⭐ Head circumference (HC) equals Chest circumference (CC) at 1 year of age. Before 1 year, HC > CC; after 1 year, CC > HC.

Infant length measurement using an infantometer

Weight Velocity - Packing on Pounds

Initial 10% weight loss (physiologic); regained by day 10-14.
Daily gain: ~25-30 g/day for the first 3 months, then slows.

Milestones (Birth Weight x N):

Doubles (2x): 5 months
Triples (3x): 1 year
Quadruples (4x): 2 years
5x: 3 years
7x: 7 years
10x: 10 years
Formula (2-6 yrs): Weight (kg) ≈ $ (Age_{yrs} \times 2) + 8 $

⭐ Weight is the most sensitive indicator of acute malnutrition (wasting) and the first parameter to show recovery.

Height & Length - The Upward Stretch

At Birth: Average length is 50 cm.
Key Milestones:
- 1 year: 75 cm (↑ 50% from birth)
- 2 years: 90 cm
- 4 years: 100 cm (Doubles birth length)
Height Estimation Formula (2-12 years):
- $Height (cm) = (Age \text{ in years} \times 6) + 77$
Mid-Parental Height (Target Height):
- Boy: $[(Father's Ht + Mother's Ht)/2] + 6.5 cm$
- Girl: $[(Father's Ht + Mother's Ht)/2] - 6.5 cm$

⭐ Measure supine length until age 2, then standing height. Supine length is typically > standing height by ~1 cm.

Measuring infant supine length using an infantometer

More Milestones - Head, Teeth & Bones

Head Circumference (HC):
- At birth: 35 cm
- At 1 year: 45 cm
- At 2 years: 48 cm
- Represents intracranial volume & brain growth.
Fontanelle Closure:
- Posterior (triangular): 6-8 weeks
- Anterior (diamond): 18-24 months

Infant skull with anterior and posterior fontanelles

Dentition (Teeth):
- First tooth (lower central incisor): 6-8 months
- 📌 Mnemonic for temporary teeth count (<2 yrs): $Age (months) - 6$
- Primary dentition (20 teeth) complete by 2.5-3 years.

⭐ The first permanent tooth is the 1st Mandibular Molar ("Six-year Molar"), erupting at 6 years, often mistaken for a milk tooth.

Bone Age:
- Best indicator of physiological maturity.
- Assessed by X-ray of non-dominant (usually left) hand & wrist.
- First carpal bones to ossify: Capitate & Hamate (4-6 months).

High‑Yield Points - ⚡ Biggest Takeaways

Weight typically doubles by 5 months, triples by 1 year, and quadruples by 2 years.

Length increases by 50% at 1 year and doubles by 4 years.

Head circumference equals the chest circumference at 1 year of age.

The fastest velocity of growth occurs during infancy, followed by the pubertal growth spurt.

Bone age is the most reliable measure of skeletal maturity and physiological development.

Mid-parental height is the best predictor for a child's target adult height.

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