USMLE Step 3 Medical Prep practice questions and answers 2026. Tap an option to test yourself — you'll see the correct answer and a plain-English explanation for every question. Free, no login.
Q21A 14-month-old boy is brought to the office by his parents for a well-child visit. The parents express concern that he is not yet walking independently and is only saying 'mama' and 'dada.' They report that he can pull to stand and cruise along furniture but does not take independent steps. He feeds himself finger foods and uses a pincer grasp. He waves bye-bye and plays peek-a-boo. His older sibling walked at 11 months. Medical history is unremarkable; the child was born at term via uncomplicated vaginal delivery. Physical examination shows no dysmorphic features. Neurologic examination reveals normal tone and strength. You perform a standardized developmental screening tool, which shows age-appropriate results in all domains. After explaining typical developmental variations and documenting the parents' concerns, which of the following is the most appropriate next step in management?
✓ Correct answer: D. Schedule a follow-up visit in 4–6 weeks to reassess motor milestones and provide anticipatory guidance on injury prevention
The correct approach documents parental concerns, acknowledges typical variation, and arranges short-term monitoring (4–6 weeks) while the screening is normal. This balances parental anxiety with watchful waiting, provides structured follow-up during any referral lag, and offers anticipatory guidance. Immediate referral is premature given the normal screening and the child's intact skills in other domains. Reassuring without follow-up ignores the parents' concern and misses documentation of their input. Waiting 6 months is too long when parents are actively worried. Repeating the screening at the same visit adds no new information and delays action.
Q22A 6-month-old girl is brought to the office for a routine well-child visit. The parents report that she seems 'floppy' compared to her older brother at the same age. She has poor head control when pulled to sit and does not bear weight on her legs when held upright. She does not roll over in either direction. The parents note that she does not seem to track moving objects consistently and does not turn her head toward sounds. She was born at 38 weeks' gestation via cesarean delivery for breech presentation. Birth weight was 2.9 kg (6 lb 6 oz). She is breastfed exclusively. Temperature is 37.0°C (98.6°F), pulse is 120/min, and respirations are 32/min. Physical examination shows generalized hypotonia with decreased resistance to passive movement. Deep tendon reflexes are 1+ and symmetric. The infant does not visually fix on the examiner's face or follow a bright red toy moved across her visual field. She does not turn toward a rattle shaken near her ear. Which of the following is the most appropriate next step in management?
✓ Correct answer: A. Urgent referral to pediatric neurology for comprehensive evaluation of hypotonia and sensory deficits
Persistent hypotonia combined with poor visual tracking and absent auditory response are red flags requiring urgent neurology referral. These findings span multiple domains (motor, vision, hearing) and suggest a central nervous system disorder, metabolic condition, or genetic syndrome. Waiting for the 9-month visit delays critical evaluation. Ophthalmology alone does not address the hypotonia and hearing concerns. Physical therapy without diagnosis may miss a treatable underlying condition. Repeat developmental screening at the same visit will not change the examination findings that mandate referral.
Q23A 28-year-old woman, gravida 2 para 1, comes to the office for her first prenatal visit at 10 weeks' gestation. She plans to continue working full-time throughout her pregnancy. Her previous pregnancy was uncomplicated, and she delivered a healthy infant at term 3 years ago. She has no chronic medical conditions and takes only a prenatal vitamin. She asks about recommended vaccinations during pregnancy. It is early October, and influenza activity has been reported in the region. She received an inactivated influenza vaccine 14 months ago. She recalls receiving a tetanus booster approximately 6 years ago but is unsure whether it contained pertussis vaccine. The table below summarizes current vaccine recommendations during pregnancy. Vaccine First Trimester Second Trimester Third Trimester Notes Inactivated Influenza Recommended during flu season Recommended during flu season Recommended during flu season Any trimester if flu season Tdap (Tetanus, Diphtheria, Pertussis) Not routinely given Not routinely given Recommended at 27–36 weeks Optimal timing for neonatal protection Live Attenuated Vaccines (MMR, Varicella) Contraindicated Contraindicated Contraindicated Avoid during entire pregnancy
✓ Correct answer: C. Administer inactivated influenza vaccine today; plan Tdap at 27–36 weeks
Inactivated influenza vaccine is recommended in any trimester during flu season, so it should be given now at 10 weeks. Tdap is optimally administered at 27–36 weeks each pregnancy to maximize neonatal antibody transfer. Waiting until the third trimester for influenza vaccine misses early flu season protection. Giving both today is suboptimal because Tdap is not yet at the recommended gestational window. Deferring all vaccines risks missing flu season entirely and delays maternal pertussis immunity. Live vaccines are absolutely contraindicated during pregnancy.
Q24A 3-year-old boy is brought to the office for a routine well-child visit. The parents report that he eats a varied diet but is 'smaller than other kids his age.' He was born at term with normal birth parameters. He has been healthy with no chronic illnesses. Developmental milestones have been age-appropriate. Physical examination shows a well-appearing child with no dysmorphic features. Growth measurements over the past 18 months are plotted on standardized U.S. growth charts and shown in the table below. Age (months) Weight-for-Age Percentile Length/Height-for-Age Percentile BMI-for-Age Percentile 18 45th 50th 40th 24 35th 48th 25th 30 20th 45th 10th 36 15th 42nd 8th
✓ Correct answer: E. Evaluate for underlying causes of growth deceleration given downward crossing of multiple percentile curves
The child shows progressive downward crossing of weight and BMI percentiles (45th→15th for weight, 40th→8th for BMI) over 18 months, indicating growth deceleration that warrants evaluation for malabsorption, endocrine disorders, or chronic illness. Height percentile is relatively stable, but weight and BMI declines are concerning. Reassurance is inappropriate when percentiles are crossing downward. Waiting 6 months delays investigation of a concerning trend. Referral to endocrinology is premature before basic laboratory workup. High-calorie supplementation without evaluation may mask an underlying disorder.
Q25A 2-week-old girl is brought to the office for a newborn follow-up visit. The parents are first-time parents and ask for guidance on keeping their daughter safe at home and during car travel. The infant was born at term via uncomplicated vaginal delivery and is breastfeeding well. The parents live in a two-story home and have purchased a convertible car seat. The father smokes cigarettes but reports he only smokes outside the house. The mother's brother died in a house fire when she was a child, and she is anxious about fire safety. Physical examination shows a well-appearing infant with normal vital signs and age-appropriate reflexes. Which of the following is the most appropriate safety counseling for this family?
✓ Correct answer: B. Keep the infant rear-facing in the car seat until at least age 2 years and establish a smoke-free home environment
Current recommendations advise rear-facing car seats until at least age 2 or per manufacturer height/weight limits, as this provides optimal head and neck protection. Smoke-free home counseling is critical because thirdhand smoke residue on clothing and surfaces still exposes infants to toxins. Forward-facing at 1 year is outdated guidance. Installing smoke detectors is appropriate but does not address the car seat question. Bassinets are safe for supervised sleep but co-sleeping increases SIDS risk. Room-sharing without bed-sharing is recommended.
Q26A 20-month-old boy is brought to the office by his mother for a routine well-child visit. She reports that he is not yet speaking in two-word phrases and does not point to objects of interest. She has completed a validated developmental screening questionnaire (Ages and Stages Questionnaire), which shows scores in the normal range for all domains. However, the mother states, 'I just feel like something is not right with his development compared to other children his age.' She mentions that her nephew was diagnosed with autism spectrum disorder and she is worried her son may have similar issues. Physical examination shows a healthy-appearing toddler who makes inconsistent eye contact and does not respond when his name is called. Which of the following is the most appropriate next step in management?
✓ Correct answer: D. Refer for comprehensive developmental evaluation despite the normal screening results
Parental concern has high predictive value for developmental disorders and should prompt further evaluation even when screening tools are normal. The combination of maternal worry, family history of autism, poor eye contact, and absent response to name warrants referral. Overreassuring when a parent expresses concern dismisses valid input and may delay diagnosis. Repeating the same screening tool will likely yield the same result. Waiting 6 months risks missing the critical early intervention window. Autism-specific screening is appropriate but should accompany, not replace, comprehensive evaluation.
Q27A 22-month-old girl is brought to the office because her parents are concerned about her language development. She says only 10–15 single words and does not combine words into phrases. She can follow simple one-step commands such as 'give me the ball' but cannot follow two-step commands. The parents report that she plays alongside other children at daycare but does not interact with them directly. She enjoys playing with toys, makes good eye contact, and points to objects she wants. She can stack four blocks, feed herself with a spoon, and remove her shoes. Medical history is unremarkable. Physical examination shows a well-appearing child with normal hearing screen results. The table below compares the child's current milestones to typical 18–24 month expectations. Domain Patient's Skills Expected by 24 Months Expressive Language 10–15 single words, no phrases Two-word phrases, 50+ words Receptive Language Follows one-step commands Follows two-step commands Social Interaction Parallel play, good eye contact, points Parallel play, beginning cooperative play Fine Motor Stacks 4 blocks, uses spoon Stacks 6+ blocks, turns pages Gross Motor Walks well, kicks ball Runs, walks up stairs with rail
✓ Correct answer: A. Refer to speech-language pathology for isolated expressive language delay
The child demonstrates isolated expressive language delay with intact social skills (eye contact, pointing, parallel play) and normal receptive language, motor, and hearing. This pattern is consistent with a 'late talker' rather than autism spectrum disorder, which would show social communication deficits. Speech therapy referral is appropriate. Comprehensive autism evaluation is not indicated given strong social skills. Watchful waiting until age 3 delays early intervention. Audiology referral is unnecessary since hearing screening was normal. Developmental pediatrics is premature before speech therapy trial.
Q28A 5-year-old boy is brought to the office for a pre-kindergarten physical examination. Immunization records show he received DTaP doses at 2, 4, and 6 months of age, but his parents moved to another state and he missed his 15–18 month booster. He has had no doses since 6 months of age. He has no known allergies and has been healthy. The parents want to complete his immunizations before school entry. Physical examination shows a well-appearing child with normal vital signs. According to current CDC catch-up immunization guidelines, which of the following is the most appropriate DTaP vaccination schedule for this patient?
✓ Correct answer: C. Administer DTaP dose 4 today; administer dose 5 at least 6 months later at age 5–6 years
The child received three primary DTaP doses but missed the 15–18 month booster (dose 4). Current catch-up guidelines require dose 4 now (minimum 6-month interval from dose 3 is satisfied) and dose 5 at 4–6 years with at least 6 months between doses 4 and 5. Giving both doses today violates minimum interval requirements. Waiting until age 6 for dose 4 delays needed immunity. Administering dose 5 in 4 weeks does not respect the 6-month minimum interval. The 5-dose series is required; stopping at 4 doses is incomplete.
Q29A 10-month-old girl is brought to the office for a routine well-child visit. The parents ask about introducing new foods. The infant currently drinks formula and eats pureed vegetables, fruits, and rice cereal. She has no known food allergies. The parents have been advised by relatives to avoid certain foods until the child is older. The mother's sister had a severe anaphylactic reaction to peanuts as a child. The parents ask specifically about when they can introduce honey, cow's milk, and peanut-containing foods. Which of the following nutritional guidance recommendations is most appropriate?
✓ Correct answer: E. Avoid honey until 12 months; introduce peanut-containing foods now; wait until 12 months for cow's milk as a beverage
Honey should be avoided until 12 months due to infant botulism risk from Clostridium botulinum spores. Cow's milk as a primary beverage is not recommended until 12 months, though small amounts in food are acceptable. Peanut-containing foods should be introduced around 6 months (especially with family history of allergy) to reduce allergy risk. Introducing honey at 10 months risks botulism. Cow's milk before 12 months increases risk of iron deficiency and renal solute load. Delaying peanut introduction to 3 years is outdated and increases allergy risk.
Q30An 18-month-old boy is brought to the office because of parental concern about developmental regression. The parents report that he could say 10 words at 15 months but now uses only 3 words. He previously walked well but now trips frequently and seems unsteady. He has lost interest in playing with toys and often stares blankly. Appetite has decreased and he has lost 0.5 kg (1.1 lb) over 2 months. He was born at term with normal development until 15 months. Physical examination shows a thin, pale child with poor eye contact. Weight has dropped from the 40th to the 15th percentile; length remains at the 50th percentile. Neurologic examination shows generalized hypotonia and brisk deep tendon reflexes. He does not respond to his name. The table below outlines the recommended evaluation approach. Referral/Evaluation Priority Level Rationale Pediatric neurology Urgent Regression and abnormal tone/reflexes Developmental pediatrics Urgent Multidomain regression assessment Metabolic/genetic workup Urgent Rule out inborn errors, storage diseases Nutrition assessment High Weight loss crossing percentiles Audiology Routine Assess hearing as part of comprehensive evaluation
✓ Correct answer: B. Urgent neurology and developmental pediatrics referrals with concurrent metabolic workup and nutrition assessment
Developmental regression (loss of language and motor skills) combined with abnormal neurologic findings, poor growth, and behavioral changes requires urgent multidisciplinary evaluation. Neurology addresses tone/reflex abnormalities, developmental pediatrics coordinates comprehensive assessment, metabolic workup screens for treatable conditions (e.g., leukodystrophies, storage diseases), and nutrition addresses growth failure. Deferring neurology delays critical diagnosis. Autism evaluation alone misses the regression and neurologic signs. Lead screening and iron studies are appropriate but insufficient for this complex presentation. MRI without specialist coordination may miss clinical context.
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