In women, plasma LH is significantly influenced by the menstrual cycle. However, some sleep modulation of LH levels occurs because the LH pulse frequency slows during sleep. In the early follicular and early luteal phases, the LH pulse amplitude actually increases, although the frequency decreases, and the nocturnal LH pulse frequency slowing becomes more evident. In middle and late follicular and luteal phases, this slowing is less apparent or absent. In postmenopausal women, FSH and LH levels are elevated without circadian variation.