Mothers are now programmed to believe that everything they do affects the welfare of their children - for better and for worse. Plenty of chat and the right stimuli as babies will make them more intelligent in later life; cruel words or neglect may land them in therapy or turn them into criminal delinquents. Smoking and alcohol are well known health risk factors for babies. A deficiency in folic acid in the first few weeks of a foetus's life can cause neural damage and even spina bifida... and so on.

Now, a spate of research into the effects of diet on a woman at about the time of conception is ladling on yet more guilt before she even gets to shag the dad. It seems that a woman's health and diet in the hours before and after conception - before she may even realise she's pregnant - appears to have a profound affect on her baby's long-term health.

Research findings from the University of Southampton, released last week, suggest that female rats briefly starved of protein shortly after conception have offspring with a higher rate of defects. Their female offspring are underweight at birth, while the males have high blood pressure, shrunken livers and enlarged kidneys. Research at Queen's University in Belfast, also released last week, suggests that the official advice of four units of alcohol per week for pregnant women may be under-cautious, for the mildest tipple may affect the foetus's nervous system. Research at St Thomas's Hospital in London, released earlier this month, seemed to show that eating too much fat and too little protein can create cardiovascular disease, regardless of how healthily the child lives after birth. Yet more research, from the University of North Carolina, has shown that gum disease can be as harmful to an unborn child as smoking regularly, for women with severe gum disease are seven times more likely to have a premature baby with low birth weight than those without.

Then there is the rather thorny issue of toxins - harmful chemicals in the environment, pesticides, additives and hormones in our food - that build up in a woman's fat tissues over the years and get passed onto the foetus through the placenta and to the baby in breast milk. According to the World Health Organisation, people should ingest a maximum of 10 nanograms of polychlorinated chemicals and dioxins a day. Yet babies in western Europe, at two months old, are taking in on average 170 nanograms a day from their mothers' milk. (Natural birth advocate Michel Odent has devised a detoxifying regime for prospective parents to maximise the health chances of their as yet unconceived child.)

Clearly there is bound to be a link between the diet of a mother and the health and welfare of her unborn child when she is manufacturing another human being. She "eats for two", with the growing foetus hijacking valuable nutrients such as calcium away from the mother to ensure its own healthy development. But how are women to differentiate between what may be significant and irrelevant when they understandably do not want to do anything that may harm their unborn child?

Firstly, the experiments on protein deficiency were carried out on rats and there is no guarantee that we behave in the same way. Secondly, most of this research has been conducted on small samples and is by no means conclusive. Thirdly, and perhaps more importantly, everything we do or consume and perhaps even feel is bound to have some sort of an effect on growing children but if we stop to analyse all this and attempt to control it we drive ourselves mad with self reproach and risk, reverting to the dark old ages of superstition. My grandmother always maintained that my mother was born with a missing ear lobe because a bullet had grazed her own ear when she was pregnant. However, that perverted gene has jumped a generation and affected one of my nieces proving, perhaps, that the cause lay elsewhere.

Living beneath an electricity pylon or near a nuclear power plant may increase the chances of cancer. Walking through busy streets in all likelihood increases respiratory diseases and asthma. Driving a car through rush hour traffic or working in a stressful job must raise a pregnant woman's blood pressure and any form of emotional distress will provoke adrenalin in both mother and baby. But this is modern life - we cannot avoid potential dangers and live enveloped in cotton wool. It won't be long before scientists find a tenuous link between excessive consumption of chocolate biscuits and hair loss or jogging and the shape of a babies nose. Diet in pregnant women is more balanced today than it has ever been. Babies are born fatter and healthier than ever, and more survive until adulthood than ever before in history. We know more about their nutritional needs, but we still indulge them with packets of fat-laden crisps, yoghurt pots heaving with unnecessary sugar and junk food riddled with additives. How can science disentangle genetic factors and the unhealthier ways we live our lives from the effects of a pregnant woman's behaviour on her unborn child? There is no way of knowing how many health problems are genetically programmed and beyond our control or the direct result of diet in pregnancy. This thirst for research into the impact of maternal behaviour on the foetus may equip some women with greater knowledge about how best to safeguard her baby's interests but the net effect is yet more guilt, as well as an uneasy sense that one can control the whole process of reproduction. Yet so much of it is still mysterious and down to chance.

Clearly, any woman longing for a child wants to maximise the health and safety of her unborn child. But the danger is that there is so much that is beyond her control that all she may be left with is an encroaching sense of inadequacy, and what sort of start does that give to mother and child? Mother's matter, a great deal. If this research genuinely empowered them to be better mothers without cranking up all those feelings of guilt and inadequacy then it would be genuinely useful. But we're human too - and fallible. We all need that odd drink to lift the spirits, a bag of chips or a bar of chocolate for occasional comfort, and often pregnant women smoke because life is tense and stressful rather than the calm oasis that medical researchers and natural birth activists maintain it should be. Women do not exist just for the sake of reproduction. They live with the stresses and conundrum of modern life and inevitably they pass some of that on to their children.