Experimental: Mirtazapine Treatment Arm

Subjects will be administered the initial dose of mirtazapine, with dosage progressively increased over the course of the study. The initial dose of mirtazapine is 15 mg tablet, once per day. The dose will be increased weekly as tolerated up to 45 mg per day. The dose will be increased by 15 mg each week if the lower dose is tolerated without significant side effects. That is to say, the subject will take 15 mg/day every day for the first week, 30 mg/day every day for the second week, and 45 mg/day every day for the third week, with the option of the subject continuing the medication for the remainder of the pregnancy. If subjects choose to discontinue the mirtazapine, there will be a tapering regimen: if a patient is taking 45 mg at the end of week 3, they will begin a taper (by week) of 30 to 15 to 7.5 to 0 mg. If they relapse or has discontinuation symptoms, the previous effective dose will be given. They may attempt to taper again with the same approach.