Hi Twitchy and S*F -
from my personal experience I would say that a referral to a psychiatrist, if possible one who is specialized in matters such as mood disorders and pregnancy, would be advisable here (a GP can do that). GP's in general don't really know that much details about the profiles of all available types of psychotropic medicine. It's not their fault, they have to deal with such a bewildering array of different illnesses that they work 'in breadth' rather than in 'depth', so to speak.
And: it is very understandable that women are wary of using mood altering substances whilst being pregnant, and during breast-feeding. The risks of alcohol use and smoking are well known, these days. Of course, illicit drugs are out of the question too.
With antidepressants, it's more complex. People with mood disorders tend to have a pretty high level of stress, continuously or frequently. They have disbalances in hormones and neurotransmitters, caused by stress and depression. For instance, their levels of cortisol are higher (the stress hormone). Freely available serotonin tends to be lower. And there are more such abnormalities. One could argue that medication should be lowered or stopped, but then the changes I just described might have an impact on the foetus or the newborn of their own. When these abnormal levels are successfully reversed by antidepressants, that might be beneficial for mother and child. So it's a matter that must be carefully considered by an expert.