The Effects of Prenatal Stress on Child Behavioural and Cognitive Outcomes Start at the Beginning

Introduction

The importance of development during the fetal period is well established with regards to the association between the baby’s growth in the womb, and later vulnerability to physical disorders such as cardiovascular disease and other aspects of metabolic syndrome.¹ It is now clear that environmental effects on fetal development are important with respect to emotional, behavioural and cognitive outcomes too. Animal studies have shown that stress during pregnancy can have long lasting effects on the neurodevelopment of the offspring.²

Subject and Research Context 

Many groups around the world are studying how the emotional state of the mother during pregnancy can have long-lasting effects on the psychological development of her child.^3-4 Some are using large population cohorts, which have the advantage of being able to statistically allow for many confounding factors including postnatal maternal mood.⁵ Others are smaller observational studies which can examine the child in more detail.⁶ Stress is a generic term which includes anxiety and depression, but also includes distress due to poor relationships or the response to an acute disaster. All these have been shown to be associated with altered outcome for the child.

Key Research Questions

What type and degree of prenatal stress have an effect on the fetus and the child? What are the gestational ages of vulnerability for different outcomes? What are the range of effects on the child and how long do they last? How does prenatal stress interact with genetic vulnerabilities? How are the effects of prenatal stress moderated by the nature of the postnatal care. How do outcomes vary with different ethnic groups and in different parts of the world?⁷

Recent Research Results  

Many independent prospective studies have now shown that if a mother is stressed, anxious or depressed while pregnant, her child is at increased risk for having a range of problems, including emotional problems, ADHD, conduct disorder and impaired cognitive development. Both altered brain structure⁸ and function⁹ have been shown to be associated with prenatal stress, and also the mother’s experience of early childhood trauma.¹⁰ While genetic transmission and the quality of postnatal care are likely to contribute to some of these findings of association, there is good evidence that there is a causal influence of the mother’s emotional state while pregnant also. Some studies have found stronger associations with prenatal maternal mood than paternal.¹¹ Several large cohort studies have found associations independent of possible confounding factors, such as birthweight, gestational age, maternal education, smoking, alcohol consumption, and most importantly, postnatal anxiety and depression.⁵ Thus, although the mother’s postnatal emotional state and the quality of early postnatal care are clearly important for many of these outcomes, the evidence suggests that there are substantial prenatal effects also.

We have shown that, within a normal population, the children of the most anxious mothers during pregnancy (top 15%), had double the risk of emotional or behavioural problems, compared with the children of the less anxious mothers.⁵ Most children were not affected, and those that were, were affected in different ways. However a doubling of risk is of considerable clinical significance. Several studies are finding that boys and girls can be affected in different ways.3 There are gene environment interactions too, in that a child with a specific genetic vulnerability is more likely to be affected in a particular way.¹²

It is clear that it is not just toxic or extreme prenatal stress that are important, as several studies have shown that problems such as daily hassles, pregnancy specific anxiety or relationship strain⁶ can have an adverse effect on the developing fetus. Effects of acute disasters such as 9/11¹³ have also been demonstrated. Different studies have shown different gestational ages of vulnerability. This may vary for different outcomes. Increased vulnerability to schizophrenia has been found to be associated with extreme stress in the first trimester.¹⁴ The risk for other outcomes, such as ADHD, has been found to be associated with stress later in pregnancy.⁵

The mechanisms underlying all this are just starting to be understood; altered function of the placenta, allowing more of the stress hormone cortisol to pass through to the fetus, may well be important,¹⁵ as may the function of the maternal immune system.¹⁶

Research Gaps

It has been suggested that a small degree of stress is actually beneficial for child outcome, as DiPietro has shown for motor and cognitive development.¹⁷ It may be that different outcomes are affected in different ways; for example prenatal stress may cause both a more rapid physical development and more anxiety in the child.⁴  Much remains to be understood about what types of stress, and at what level, stress has effects on the developing fetus. We know little about the effects of different types of work stress during pregnancy. We need to know more about gestational ages of vulnerability for different outcomes. There are research gaps in our understanding of the contribution and interactions between prenatal stress and the genetic vulnerabilities of both mother and child. We also need to know more about to what extent, and at what times, it is possible for sensitive postnatal care to counteract the effects of prenatal stress.

Conclusions

Maternal stress during pregnancy increases the risk of the child having a range of altered neurodevelopmental outcomes. The stress can be of different types, and at least for some outcomes, there seems to be a linear dose response effect. Not all children are affected, and those that are, are affected in different ways. The gestational age of vulnerability probably differs for different outcomes. It is of interest to view all this in terms of our evolutionary history. In a stressful environment it may have been adaptive for our ancestors to have children who were more vigilant (anxious) or with readily distracted attention (ADHD), and possibly with more rapid motor development. But in our modern world several of these changes can be maladaptive,  and cause problems for the child and their family.

Implications for Parents, Services and Policy

The implications of this research are that if we want the best outcomes for our children we need to provide the best possible emotional care for pregnant women. There needs to be more public health education about this issue, and pregnant women encouraged both to look after themselves emotionally, and to seek help if needed. At present most anxiety and depression in pregnant women is undetected and untreated. We need to make sure that pregnant women are sensitively questioned when they first come into contact with health professionals about their emotional history and current state. It is important to note that it is not just diagnosable disorders that can affect fetal development, but a range of symptoms of stress, anxiety and depression, including a poor relationship with the partner. Appropriate personalized help should be instituted for each woman. This has the potential to prevent a range of neurodevelopmental problems arising in a clinically-significant proportion of children.

References

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