What is the next step if ultrasound indicates the presence of a uterus in a patient evaluated for primary amenorrhea?

In a patient with primary amenorrhea and an ultrasound indicating the presence of a uterus, measuring serum FSH (follicle-stimulating hormone) levels is the logical next step. This is because the presence of a uterus suggests that the individual may have functional ovaries and a potential for estrogen production.

Assessing FSH levels helps determine the functional status of the ovaries. High levels of FSH would indicate ovarian insufficiency or failure, suggesting that the primary amenorrhea could be due to conditions such as Turner syndrome or premature ovarian failure. Conversely, low or normal FSH levels may indicate a central cause of amenorrhea, such as hypothalamic or pituitary disorders.

This evaluation is crucial for the overall management and understanding of the patient's condition, aiding in further diagnosis and treatment options.