Fetal programming is, simply, how early life events and environments affect later life of the fetus. Basically, DNA is set at conception - that doesn't change. But the way
… it folds up (and which bits are too 'folded' to be of any use) is able to change. This is currently a really big field in research at the moment! After all - if you can prevent people from getting serious health issues caused by events that happened before they were even born (or shortly thereafter), then you can save a lot of grief and money in later health (and associated emotional) costs! The fetus is 'plastic' - it can adapt to some of the things life throws at it. If a mother is in a country with little food, the fetus is also affected by malnutrition, and can (particularly better in girls) adapt to this to prepare for postnatal (after birth) life. They are born able to make better use of small amounts of food ('thrifty phenotype' for survival). But this means that if there's actually a lot of food around when they are born, they can end up with obesity, cardiovascular problems, and several other issues, such as immune system alterations. For example, see David Barker's work, or the effects of the Dutch Winter Famine on the later health of individuals who were born during or shortly after the famine - malnutrition in utero (during gestation) resulted in these individuals having higher risks of cardiovascular disease. (MORE) 
