A 4-month-old is brought by her mother for the child’s well-check. The mom has no complaints but thinks the baby’s

A 4-month-old is brought by her mother for the child’s well-check. The mom has no complaints but thinks the baby’s head “looks big.” The child was born at 35 weeks, so gestationally she is only 3 months old. The mother says the child is eating well, has started cooing, and has a social smile. The baby’s dad seems to have a large head as well, so she thought it might be normal for his side of the family. The baby’s head circumference at the 2-month checkup was in the 85th percentile, but now it is in the 98th percentile. Given this concern, testing is needed. The baby has crossed 2 percentile lines on the growth chart and has the added risk factor of being premature. Which test is often easiest to obtain in most primary care settings and is effective in diagnosing the problem with limited risk? A. Head CT without contrast B. Head MRI C. Lumbar puncture D. Head ultrasound