Birth isn’t destiny

How far do we inherit health problems from our parents and grandparents?

Sure, we are in many respects subject to what is in our genes. But if you were born with low birth weight for another reason, for example, because your mother was malnourished or smoked during pregnancy, will your own poor start to life affect the growth of your children?

The good news is probably not, or at least not much.

That’s what we found when investigating low birth weight among Aboriginal infants, the results of which are published in the Lancet Global Health journal. It means that poor fetal growth and the lifelong consequences of poor fetal growth that disproportionally impact Aboriginal people can be fixed within a generation if we can improve maternal health in today’s pregnancies.

Does birth weight matter?

Low birth weight infants account for the majority of infant deaths. Low birth weight is also associated with poor development in childhood and a range of physical and mental health problems throughout the life course.

Birth weight is known to be affected by genes and environmental factors, such as maternal smoking, diabetes or infection. And another cause has been proposed – the health of a fetus may be affected by the health of previous generations due to what is called fetal programming.

What is Fetal Programming?

Fetal programming refers to changes in a fetus in response to adverse conditions inside the womb, like poor nutrition, and these changes may have lifelong effects.

An example of this followed the Dutch Hunger Winter, a famine which occurred near the end of World War II, when the Nazis restricted food in the western region of the Netherlands. Children whose mothers were pregnant during the famine were born smaller, on average, than those unaffected by famine and they also had worse health in adulthood.

But are these health impacts on unborn children passed on when these children grow up and have children of their own? This question is difficult to answer because, in addition to the possibility that fetal programming in one generation may affect the next, there are other reasons why parents and their offspring may have similar health. Parents share genes with their offspring and they may also share environmental exposures.

The question is further complicated by the lack of routinely collected biological indicators of the conditions experienced by a fetus. Instead, birth weight is often used as a proxy for fetal health.

In humans, ‘natural experiments’ like the Dutch Hunger Winter and family-based studies like comparisons of cousins can help untangle these genetic, environmental and fetal programming effects. But studies of the potential trans-generational effects of the Dutch Hunger Winter on birth weight have reached different conclusions.

While children whose mothers were subject to famine were more likely to have low birth weight, it is less clear whether the famine affected the following generation – for example, one study found a difference in the birth weights of the next generation (whose maternal grandmothers were pregnant during the famine), but another study found no effect.

Why study Aboriginal Western Australians?

It has likewise been hypothesised that indigenous peoples and people from nations which have undergone rapid transitions to ‘Western’ lifestyles with a higher risk of obesity, may be particularly affected by fetal programming.

The theory is that fetuses whose mothers had inadequate nutrition during pregnancy may be ‘prepared’ for a life of privation, which may put them at a particularly high risk of obesity and diabetes if instead their postnatal diet is high in calories.

For many Aboriginal communities in Western Australia, major changes in lifestyle have occurred relatively recently. As late as the middle of the 20th century, many were dependent on (inadequate) rations, and today the diet in some communities, like in the Great Sandy desert, continues to include gathered foods.

Aboriginal infants have for generations been at higher risk of low birth weight. In our study of over 12,000 Aboriginal births in Western Australia between 1998 and 2011, 17 per cent were born small for gestational age (having low birth weight given the number of weeks of pregnancy) compared to 10 per cent of all Australian births, Aboriginal and non-Aboriginal combined.

With this history of low birth weight and recent changes in lifestyle, we would have expected that if the effects of poor fetal health accumulate across generations, we would see this among Aboriginal Western Australians.

What we found

We found that low birth weight mothers were indeed more likely to have low birth weight children. But we concluded from the evidence that this association was explained by shared genetic and environmental factors.

While we couldn’t rule out that a poor fetal environment affects not just one, but two generations, any effect on the second generation is likely to be very small compared with, for example, the effect of their mother smoking.

What this means is that a woman born with a low birth weight, perhaps because her mother had poor health, isn’t likely to be passing on the distress she suffered as a fetus to her own children. Despite generations of low birth weights among Aboriginal infants, improvements can happen within a single generation if we focus on the known, important, modifiable causes of low birth weight in today’s pregnancies.

In a sense, mothers start with a clean slate.

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