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Child development: the first 1000 days

Baby and toy

Research by leading Australian scientists has found that what is ‘learned’ both in the womb and throughout the first few years of life has profound consequences over the course of a life.

The First Thousand Days1  has shown children are affected in multiple ways, including through biology, their experiences, environment and diet, and their parent’s health and lifestyle during pregnancy.

Most fascinating however is that starting from conception, the foetus is actively responding to changes in the environment, using cues provided by the mother’s physical and mental state to ‘predict’ the kind of world they will be born into and altering their bodily structures accordingly. 

First Thousand Days lead author Dr Tim Moore says this adaptation can be either beneficial or detrimental, depending on the child’s relationships and environments.

“Children need to feel calm, safe and protected. When this attachment process is interrupted, the child’s brain places an emphasis on developing neuronal pathways that are associated with survival, before developing those that are essential to future learning and growth.”

The role of epigenetics and synaptic pruning

The science describes two central mechanisms that underlies this adaptation process: epigenetics (whereby the genes listen to the environment) and synaptic pruning (whereby the brain listens to the environment).

What this means is that our genes alone do not determine our characteristics but work in tandem dynamically with our environments. When this occurs the result is epigenetic change.

A child may have a combination of genes that predisposes them to a particular condition or behaviour, but never be exposed to the particular environment needed to trigger this condition so the gene remains dormant. Similarly, a child may be exposed to a particular triggering environment, but lack the genes that would predispose them to respond adversely. 

The paper states that epigenetic changes have been implicated in the development of a wide range of disorders, from cardiovascular disease to autism spectrum disorders and cognitive disorders, and may be triggered by a wide range of environmental exposures and experiences.

In humans, the epigenetic system is most sensitive to environmental influences during the period of developmental plasticity (i.e. the first 1000 days).

The periods before and just after fertilisation are highly sensitive periods. Epigenetic changes can start to occur shortly after conception. 

The research found that at conception, the egg and sperm combine their genetic material to form an embryo, whose set of genes reflects both the age and the environmental exposures of both parents. 

“During fertilisation and the first cell divisions, the embryo is highly sensitive to signals from the mother’s reproductive tract: the fluid that surrounds the embryo during its passage to the womb varies according to the mother’s nutritional, metabolic, and inflammatory states, reflecting the particular world in which she lives. The embryo has a high degree of developmental plasticity, and responds to these environmental cues by modulating its metabolism, gene expression, and rate of cell division.

"Epigenetic changes can occur throughout pregnancy. Hormones and nutrients that cross the placenta can be affected by the mother’s body composition, metabolism, and long-term lifestyle. 

“The foetus is sensitive to hormonal and other physiological indicators of maternal stress, and heightened exposure to stress in the womb is associated with greater reactivity to stress after birth, as well as longer-term problems with emotional and cognitive functioning. 

“In general, prenatal stress exposure makes children more reactive to challenge and threat. In addition, maternal stress and toxin exposure during pregnancy, and maternal-infant interactions after birth have been linked to changes in the offspring’s epigenetic state. 

“Even natural variations in the quality or quantity of maternal care can have a long-term impact on the offspring’s brain and behaviour. The prevalence of these effects suggests that epigenetic effects are a central mechanism by which environmental experiences, both positive and negative, become biologically embedded and ‘get under the skin’.”

Many challenges faced by adults, such as mental health issues, obesity, heart disease, criminality, and poor literacy and numeracy, can be traced back to pathways that originated in early childhood.
The First Thousand Days: An Evidence Paper

How experience shapes biological and neurological development

The report stresses the importance of children’s development beyond the brain to all bodily structures including the immune, gastrointestinal and cardiovascular systems.

Disadvantage can also be passed down through the generations at a cellular level, with biology changing in response to stress, poverty and other prolonged adverse experiences. These changes can be passed on to children from their parents and grandparents. Children can only develop as well as their families, communities and broader society enable them.

The paper found that new knowledge is emerging about the underlying mechanisms by which experiences shape biological and neurological development; including changes at the cellular level (telomeres), biological level (epigenetic processes), neurological level (synaptic growth and pruning), and the microbiome level. 

In particular the researchers point to a study of holocaust survivors, Yehuda and colleagues (2015) which found that genetic modifications as a result of trauma are capable of being passed onto children, affecting subsequent generations.

“Many challenges faced by adults, such as mental health issues, obesity, heart disease, criminality, and poor literacy and numeracy, can be traced back to pathways that originated in early childhood,” the paper says.

“To ensure positive health and wellbeing for current and future generations, we therefore need to focus on improving the environments and experiences of the earliest stages of development, including the prenatal period.”

Fortunately, telomere shortening can be slowed, prevented or even reversed through exposure to positive environments, so the impact of early adverse experiences or inheritance can be counteracted. Telomere maintenance occurs through the activation of telomerase, an enzyme that counteracts shortening by adding DNA and building back the chromosome end each time a cell divides.

This new way of understanding baby’s brain development is already influencing how we think about helping vulnerable and disadvantaged children. Armed with this knowledge the researchers say we can work to ensure that children born into difficult situations can receive the extra help they need to thrive.

Supporting parents

MCRI Research Group Leader in Policy, Equity and Translation Professor Frank Oberklaid says the evidence highlights that parents cannot raise healthy, happy children on their own.

"Along with loving relationships, children need safe communities, secure housing, access to green spaces, environments free from toxins, and access to affordable, nutritious foods," Professor Oberklaid says. "This requires whole-of-society efforts and appropriate investment."

While the paper stresses that the ability to alter and change the impacts of negative experiences in the first thousand days becomes more difficult as a child gets older, it is certainly not impossible to make improvements as children grow and develop.

“After 1000 days the different effects on children begins to taper off,” lead author Dr Moore says. 

“It’s not the end of the world, it just becomes harder to change. We don’t want parents to feel like ‘what have I done’, it’s about encouraging everyone to think about the importance of this time period, and how the whole of society should consider this responsibility.”

The report was prepared by the Centre for Community Child Health with researchers from the Murdoch Children's Research Institute (MCRI), and produced with the support of the Bupa Health Foundation, PwC and ARACY.

Researchers are continuing to see what else is determined in the first thousand days to provide further support and interventions to make sure children are safe and secure.


1 Moore, T.G., Arefadib, N., Deery, A., & West, S. (2017). The First Thousand Days: An Evidence Paper. Parkville, Victoria; Centre for Community Child Health, Murdoch Children’s Research Institute.