Children at risk if their mothers had stressful pregnancy
Press release issued: 28 September 2005
Children whose mothers experienced significant stress or anxiety during pregnancy have a greater vulnerability to psychological problems, even 10 years later, according to a study conducted at the University of Bristol.
Analysis of stress hormone levels in 10-year-old children has provided the strongest evidence yet that prenatal anxiety may affect the baby in the womb in a way that carries long-term implications for well-being.
The study suggests that fetal exposure to prenatal maternal stress or anxiety affects a key part of their babies' developing nervous system - leaving them more vulnerable to psychological and perhaps medical illness in later life.
The research, involving families taking part in the Avon Longitudinal Study of Parents and Children (ALSPAC) project, also known as 'Children of the 90s', has been published in the journal Biological Psychiatry.
Previous studies of animals had shown how stress in pregnancy affects the hypothalamic-pituitary-adrenal axis, the body's stress response system but until now scientists have been unable to show it affects humans in the same way.
A total of 74 children were asked to take part in the pilot study, which involved taking saliva samples first thing in the morning and three times during the day on three consecutive school days. Scientists then tested the samples for levels of the stress hormone cortisol.
Psychologist Dr Thomas O'Connor from the University of Rochester in New York then compared those results with psychological tests completed by their mothers during the last stages of pregnancy, 10 years earlier.
Dr O'Connor said: "We found that anxiety in late pregnancy was associated with higher levels of cortisol in children many years later.
"These results provide the strongest evidence to date that prenatal stress is associated with longer term impact on the HPA axis in children, a finding repeatedly demonstrated in animal investigations."
One theory suggests that anxiety or stress in pregnancy increases the mother's own levels of cortisol, which crosses to the fetus and influences the baby's brain development, notably its stress response system.
These changes to the stress response system may make children more susceptible to a range of psychological and medical problems.
Dr O'Connor said: "Findings from several human studies of children and adults suggest that elevated basal levels of cortisol are associated with psychological risk or psychological disturbance, notably depression and anxiety.
"Our findings point to a possible mechanism by which prenatal stress or anxiety may predict these disturbances into early adolescence, and possibly into adulthood.
"More work is needed now to consider why cortisol should be associated with particular forms of psychiatric disturbance, and what factors accentuate or mollify the links."
This report coincides with the announcement of a large follow-up project with the Children of the 90s study funded by the National Institutes of Health in the US.
Around 8,000 children will take part in the study to examine the mechanisms by which anxiety and stress in pregnancy may have long-term effects on psychological development in adolescence.
Families will be asked to collect saliva samples from children at the age of 14 so that scientists can examine cortisol levels and look at the longer term effects of stress on the mothers.
Dr O'Connor said that the size of the grant - more than $2 million - reflected how importantly the issue of stress during pregnancy is now seen by medical researchers.
He said: "Some scientists have suggested that prenatal stress should be viewed alongside smoking and alcohol intake in pregnancy in terms of its potential adverse effects on the fetus.
"Data from a previous study in the United States indicate that 20.9 per cent of the population of nine to 17-year-olds are affected with a debilitating mental illness.
"13 per cent are diagnosed with anxiety disorder, 6.2 per cent with a mood disorder, and 10.3 per cent with a disruptive behaviour disorder.
"Early adolescence is characterized by a marked increase in the levels of serious and persistent mental disorder, notably depression, anxiety, and substance use.
"If we can identify why this happens, the mechanisms whereby early risks lead to later psychological disturbance in the child, it will have substantial application for doctors and the health services.
"If it is the case that stress or anxiety in pregnancy has a long-term direct effect on adjustment in adolescence, then that would suggest that we might be able to intervene during pregnancy to prevent some of this."