Growth, Development and Behavioral Pediatrics
The Growth, Development and Behavioral Pediatrics domain tests whether you can plot and interpret growth, recognise the normal timing of developmental milestones, and manage common behavioral presentations. Items are usually data-driven: you are given measurements or a milestone history and asked what is normal, what needs investigation, and what needs referral.
Growth rules worth memorising
- Regain birth weight by day 10-14; double it by 4-5 months; triple by 12 months; quadruple by 2 years.
- Length rises about 50% in year one (50 to 75 cm), then 5-6 cm/year until the pubertal spurt.
- Head circumference: 34-36 cm at birth, plus about 2 cm/month for 3 months, reaching roughly 47 cm at 1 year.
- Mid-parental height: boys (father + mother + 13)/2 cm; girls (father + mother - 13)/2 cm; target range +/-8.5 cm.
- Correct for prematurity until 2 years (3 years for head circumference in the very preterm).
- Crossing two major centile lines is the red flag; a single low point on its own is not.
Milestone anchors
- Social smile 6 weeks; head control 3 months; sits unsupported 7-8 months; walks independently 12-15 months.
- Pincer grasp 9-10 months; scribbles and builds a tower of two cubes at 15-18 months.
- Babble 6-9 months; single words at 12 months; 50 words and two-word phrases by 24 months; three-word sentences at 3 years.
- Red flags: no babble at 12 months, no single words at 16 months, no two-word phrases at 24 months, any loss of skill, and hand preference before 18 months (think hemiplegia).
- Screen for autism with M-CHAT at 18 and 24 months and refer on any failed screen rather than reassuring the family.
Worked example
A 7-year-old boy is referred for short stature: height 108 cm, well below the third centile. Mother 155 cm, father 165 cm. Mid-parental height = (165 + 155 - 13)/2 = 153.5 cm, giving a target range of 145-162 cm. His height falls far below even the lower limit of the target range, so familial short stature does not explain it. Growth velocity is 4 cm/year (expected 5-6 cm), and bone age is 2 years behind chronological age. Investigate: coeliac serology, thyroid function, IGF-1, full blood count, and karyotype if a girl. Constitutional delay would show delayed bone age matching height age but a normal velocity.
Traps that cost marks
Measuring recumbent length in a child over 2-3 years; plotting a preterm infant without correction; calling a single measurement abnormal without a velocity; labelling isolated speech delay as late talking when hearing has never been tested; and interpreting head circumference without length and weight, since macrocephaly with normal growth is often familial while a rapid upward crossing needs imaging.