A fortnight after the birth, both were admitted into a psychiatric ward and Shaw's struggle to understand her depression and conquer her self- destructive urges began. Self-mutilation and anorexia, culminating in electric shock treatment, were to follow.
Now her bleak story is to be laid bare in Out Of Me (Viking Books, pounds 16), a personal account of post-natal trauma published later this month.
Its pages reveal how, although dogged by the feeling that she was somehow "putting it all on", Fiona Shaw slid quickly into a deep state of psychosis: a condition visited upon her, and one in every thousand other mothers, without apparent warning.
In starting her first book Shaw, an academic who lives in North Yorkshire, honestly admits she intended purely to exorcise some of her own demons and fears. Today she also hopes the harrowing narrative will be considered well-written and that it will help other women in the same kind of trouble.
"It has taken me a long time to write this book and reprocess it all, but I found that telling the story helped me a lot," she says.
Some of her female readers may feel the cathartic power of the book, too, given the shame and secrecy which still mask post-natal mental distress.
Even the condition's mildest form, known quaintly as The Baby Blues, was once a source of acute embarrassment to new mothers. Nowadays it is accommodated within the normal range of hazards surrounding childbirth.
The Blues were shared, we have recently learned, by such disparate celebrities as Princess Diana, Muriel Gray, Emma Forbes, Imelda Staunton and Jerry Hall. And as each public figure decides to talk about their post-natal problems, new mothers are better prepared for the huge hormonal onslaught that strikes on the fourth or fifth day following labour.
Unfortunately, the gentler form of the illness, experienced by half the mothers in Britain, has two appalling and debilitating cousins; severe depression and puerperal psychosis.
While serious depression generally slides out of the blues to take root in the enforced domesticity of child rearing, the more violent psychoses tend to set in very fast and can lead to delusions, terror or complete breakdown.
"People are ashamed of depression in general, I think," says Shaw. "But there are very specific ramifications to having a child. There is an enormous responsibility and there is, of course, a cultural expectation that everything will be fine, while in fact it can be tremendously lonely being at home as a new parent."
One of the hardest parts of the illness is the way it cuts off the sufferer from their close relatives and friends. Claire Delpech, who helped Shaw with her book and is secretary of the Association for Post-natal Illness, believes the condition is still strongly stigmatised.
"It is one of the most cursedly hidden illnesses in all social classes," she says.
"There are all kinds of illnesses it is more acceptable to have, including Aids. Even being accepted within their own family is hard for many mothers, although there are some enlightened grannies around."
Shaw agrees, suspecting that her own story will prove to have been harder to disclose to her own family than to the general reading public.
"I don't think it is necessarily the way forward for every mother to be as open about it as I have," she concedes. "I have always talked a lot and I have always used words to make sense of things. That was what was so disturbing about not being able to explain things during my treatment."
After a history as a "difficult" child, raised jointly by two sets of parents, Shaw's adult problems kicked in at a point when life at last had the trappings of security and happiness.
She had fallen in love with one of her English lecturers, married him, bought a country cottage and started a family. Perhaps, she feels in retrospect, she was overburdened by the sense of her good fortune.
"My breakdown seemed to come to me out of the blue," she says. "Yet, instead of coming from nowhere, I found through writing the book that it was very much a part of my past and of my present."
Shaw's biggest regret about her period of treatment is the way she meekly submitted to ECT, or electro-convulsive therapy. It decimated her short term memory and destroyed her ability to think throughout the illness. "I wish I had not had it. If it ever happened to me again I would take every step to avoid having ECT although, in comparison with other people's experiences, its effects on me were fairly middling. It ruins some people's whole lives."
At the mother and baby unit in the Maudesley Hospital, south London, Professor Channi Kumar argues that the effects of ECT need not be any more disorienting than those of drugs more regularly prescribed for depression.
"ECT does cause a certain amount of confusion, but used correctly, this can be minimised. Properly applied to one side of the brain and with proper anaesthetics, the business of disorientation can be reduced."
The "bad aura" around ECT is unjustified, Prof Kumar believes. "ECT does not affect the breast milk as drugs do and so it may actually be a cleaner form of treatment. I don't think we really know absolutely how it is that many of the drugs we use work either." He considers women are still not sufficiently aware of the risk of mental illness after childbirth.
"It would be quite wrong, however, to cast a pall of gloom over a family at this time. Only about one mother in a thousand becomes psychotic, while only about one in 10 develops a more serious depression." Most mothers can be treated as outpatients and never need to go to a mother and baby unit, he stresses.
Claire Delpech agrees that ECT can still regarded as an acceptable treatment of last resort. For her, the greatest improvement in treatment of the illness would be wider acceptance.
"It is wonderful that people are now talking," she says. "After Diana spoke about it we had thousands of calls from people saying they felt they could now ask for help.
"We have to get away from this idea in advertisements that a successful mother is a mother who does not allow her child to affect her life in any way."
Association for Post-natal Illness, 0171 386 0868, office hours from Monday-Friday.Reuse content