USMLE Step 1 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.
Q1A newborn is noted to have low-set ears, micrognathia, and a cleft palate. The mother reports drinking alcohol daily during the first trimester. Which of the following best describes the embryologic period when these craniofacial abnormalities most likely developed?
✓ Correct answer: D. Weeks 4-8 of gestation
Craniofacial abnormalities associated with fetal alcohol syndrome typically develop during the critical period of facial development in weeks 4-8 of gestation. This is when the facial prominences and palatal shelves form, and exposure to teratogens during this period can lead to dysmorphic features including low-set ears, micrognathia, and cleft palate.
Q2A 15-month-old child presents for a well-child visit. The parents are concerned because the child is not yet walking independently. Which of the following represents the appropriate developmental milestone for this age?
✓ Correct answer: C. Walking independently
By 15 months of age, most children should be walking independently without support. This is a key gross motor milestone that typically occurs between 12-15 months. Children who have not achieved independent walking by 18 months warrant further developmental evaluation.
Q3A 30-year-old woman is 8 weeks pregnant and is prescribed isotretinoin for severe acne. Which of the following congenital malformations is most strongly associated with exposure to this medication during pregnancy?
✓ Correct answer: B. Craniofacial abnormalities
Isotretinoin (a vitamin A derivative) is a potent teratogen that causes characteristic craniofacial abnormalities, including ear malformations, micrognathia, and cleft palate. It also causes cardiac and CNS defects. This medication is contraindicated during pregnancy due to its high risk of causing congenital malformations.
Q4A 24-week pregnant woman presents with vaginal bleeding and is diagnosed with placenta previa. Which of the following best explains how this condition affects maternal-fetal interaction?
✓ Correct answer: A. Decreased placental blood flow leading to potential fetal hypoxia
Placenta previa occurs when the placenta implants over the internal cervical os, which can lead to maternal hemorrhage when the cervix begins to dilate. This condition interferes with maternal-fetal interaction by potentially compromising placental blood flow, which can lead to fetal hypoxia and growth restriction due to decreased nutrient and oxygen exchange.
Q5A 3-year-old child has difficulty interacting with peers, demonstrates repetitive behaviors, and has delayed language development. Genetic testing reveals a mutation affecting synaptic proteins. Which of the following best describes the gene-environment interaction in this condition?
✓ Correct answer: D. Genetic mutations affect neural circuit development, while environmental factors modify expression of symptoms
Autism spectrum disorder often involves a complex interplay between genetic susceptibility and environmental factors. Genetic mutations affecting synaptic proteins can impact neural circuit development and connectivity, while early environmental exposures and experiences can influence how these genetic factors are expressed, potentially modifying the severity and presentation of the condition.
Q6During a pediatric visit, a mother reports that her 9-month-old infant becomes extremely distressed when she leaves the room, which was not the case a few months ago. This behavior most likely represents which normal developmental process?
✓ Correct answer: C. Separation anxiety
Stranger anxiety and separation anxiety typically develop around 6-9 months of age as infants begin to form specific attachments to caregivers and can distinguish between familiar and unfamiliar people. This represents normal social-emotional development and coincides with the development of object permanence - the understanding that objects (and people) continue to exist even when they cannot be seen.
Q7A 42-year-old pregnant woman undergoes amniocentesis that reveals trisomy 21. Which of the following maternal factors most likely contributed to this chromosomal abnormality?
✓ Correct answer: B. Advanced maternal age
Advanced maternal age (typically defined as age 35 or older) is the most significant risk factor for trisomy 21 (Down syndrome). The risk increases exponentially with maternal age due to aging oocytes being more susceptible to nondisjunction during meiosis, which leads to trisomy 21 in the fetus.
Q8A newborn presents with ambiguous genitalia. Laboratory analysis reveals elevated 17-hydroxyprogesterone levels. During which week of embryonic development did the pathophysiologic process leading to this condition most likely begin?
✓ Correct answer: A. Week 7
Sexual differentiation of the external genitalia begins around week 7 of embryonic development. In congenital adrenal hyperplasia (suggested by elevated 17-hydroxyprogesterone), excessive androgen production during this critical period leads to virilization of female external genitalia, resulting in ambiguous genitalia.
Q9A premature infant born at 30 weeks gestation develops respiratory distress shortly after birth. Which of the following best explains the developmental basis for this condition?
✓ Correct answer: D. Insufficient surfactant production by type II pneumocytes
Surfactant production by type II pneumocytes typically begins around weeks 22-24 but doesn't reach adequate levels until approximately 34-36 weeks gestation. Premature infants born before sufficient surfactant production are at high risk for respiratory distress syndrome due to poor alveolar stability, increased surface tension, and alveolar collapse, leading to impaired gas exchange.
Q10A 62-year-old man presents with crushing substernal chest pain radiating to the left arm that began while shoveling snow. ECG shows ST-segment elevation in leads II, III, and aVF. Which coronary artery is most likely occluded?
✓ Correct answer: C. Right coronary artery
ST-segment elevation in leads II, III, and aVF indicates an inferior wall myocardial infarction, which typically results from occlusion of the right coronary artery (RCA). The RCA supplies the inferior wall of the left ventricle in approximately 80% of people (right-dominant circulation).
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