What are the risks of taking 7.5mg of mirtazapine while pregnant and/or breastfeeding?

Unknown: Risks are unknown at this time. Talk to your doctor about the benefits you are deriving from the medicine, so you can make an informed choice.

Mirtazapine: Mirtazapine is cat. C medication, so you need to weigh benefits vs. Risk. If absolutely essential, it can be taken. If you can avoid taking it in the first trimester, i would advise you to talk to your doc about that or go on safer alternatives if those exist. It can be excreted in breast milk as well. Harmful effects are unlikely for the baby, but caution is advised.

Likely small: No pregnant or breast feeding women were included in clinical trials with mirtazepine. This is a low dose so the benefit must be weighed against any potential risk. Likely very low levels in breast milk.