The subject of extreme morning sickness has reared its head with a story this week of a young woman named Fiona Shaw, who was so ill with the condition that her baby had to be delivered two months premature, by caesarian section, and weighed a tiny 2lb 5oz. After the baby's first week of life, her weight dropped to just 2lb, the Daily Mail reported. So ginger biscuits are not, after all, an answer to everything.

Shaw suffered from a condition known as hyperemesis gravidarum, which, if we can just strip the mystery out of the medical profession for a second, means "vomiting a lot because you are pregnant". Clearly, the severity of her case was unusual - by her 28th week, she had lost 3st, having been able to swallow nothing on some days but half a biscuit. Even some weeks before the caesarean, she had been admitted to hospital with dehydration. This makes her the one in 10,000 women who suffers from severe HG - regular HG, which affects one woman in a hundred, can be treated with a variety of drugs. It is extremely unpleasant but unlikely to result in the foetus failing to thrive as Fiona Shaw's did.

A useful analogy (as well as a side effect, but that's another story) is with depression - think of morning sickness as like feeling a bit miserable; a brisk walk in the sunshine might help. And you would expect to be rid of morning sickness by the start of the second trimester. Regular HG, by contrast, is equivalent to fully fledged depression. There are various drug treatments available, most of them antiemetics.

The causes have not been definitely established, but there does seem to be a genetic component, and broadly speaking, it results from an adverse reaction to the flood of pregnancy hormones. It is possible that you might end up in hospital being given fluids by intravenous drip, but unlikely that the baby would have to be induced a long time before term. The foetus is not affected by the illness of the mother, unless she is eating so little that it is getting no nutrients at all, and then we are really talking about half a biscuit a day.

Nevertheless, HG can be unutterably demoralising, especially when accompanied, as it sometimes is, by ptyalism, a condition whereby you cannot swallow your own saliva without vomiting.

There are no home remedies specific to HG beyond those normally suggested for morning sickness, and HG sufferers are often piqued at the implication that what they are experiencing is just a bit of queasiness. However, used in conjunction with prescribed antiemetics, the following things are all said to help: taking vitamin B6; getting a lot of sleep; homeopathy; acupressure wristbands; eating little and often; only eating things that are very hot or very cold; ginger, peppermint, dry biscuits, pineapple, papaya, cantaloupe and vinegar in hot water. Should you present at the GP with symptoms of frequent vomiting and weight loss, you will probably be started off on an antihistamine. Its only nuisance is tiredness, but you will be so tired anyway, what with the malnutrition and the foetus leaching all your energy, that you might not notice. The main problem is that if you can't keep anything down, tablets won't work. Then you'll end up on suppositories, which are not only icky, they are rarely as strong.

So work on keeping that tablet down.

One of the defining symptoms of severe HG is that the drugs don't work, and there sadly isn't a whole other stable of drugs that medics are holding back for when things get really bad. One school of thought is that Charlotte Brontë probably died of severe HG, along with her unborn child. Elizabeth Gaskell identified her "sensations of perpetual nausea and ever-recurring faintness" but since, at that time and indeed until the middle of the last century, doctors thought morning sickness was psychosomatic - resulting from ambivalent feelings about becoming a mother - it could have been politeness that caused Brontë's doctor to write TB on her death certificate. Death from HG would probably be the result of kidney or heart failure.

Back to these drugs that either don't work or don't exist: there are two, basically nuclear, options, one a steroid, prednisolone, which is widely used in the US, and one an antiemetic, Zofran, which was developed for the after-effects of chemotherapy. Both of these are rarely prescribed in Britain, the first because steroid use during pregnancy has not been thoroughly enough researched to rubber stamp it, the second because it is extremely expensive. One couple managed to persuade their primary care trust that it was cheaper to prescribe Zofran than simply keep the woman in hospital for her full pregnancy, but you would need a pretty flexible and receptive PCT to emerge victorious from a conversation in which you, a layperson, dared to talk about drugs and budgets in the same sentence.

It is salutary to note that the tragedy over thalidomide - the anti-nausea drug banned for use by pregnant women in the 1960s after it was shown to be damaging the development of some foetuses - continues to echo through obstetrics. The appetite simply is not there to research pharmaceutical solutions to sickness unless things get phenomenally bad, which they only rarely do. If the drugs will not work or are unavailable, and if the HG is so severe that the mother cannot satisfy her and her baby's nutritional needs, even with IV fluids, the only other option is a termination, a heart-breaking choice considering that the woman has already been fighting the sickness for some weeks.

Morning sickness is very unpredictable: you might get it horribly for the first pregnancy and not at all for the second. Hyperemesis gravidarum, however, has a 75% chance of recurring in later pregnancies, according to one study. It really is a frightful business. Jokes about how it is a good way to keep the weight off could not be less appropriate.