30-years-old woman with a history of secondary amenorrhea for 4 months. Her lab investigation is as follow: UPT is negative. FSH- 6.2 (4.7 - 21.5mIu/ml), LH- 6.8 (1-18 mIU/dL), Prolactin 40 (< 25 ng/mL) TSH 0.4 (0.5-4.0) Which of the following is the underlying aetiology for her amenorrhea?
a) Hypothalamic dysfunction
b) Pituitary adenoma
c) Congenital hypothyroidism
d) Polycystic ovarian syndrome
e) Premature ovarian failure