Can maternal stress lower baby's IQ?

Stress during pregnancy can affect babies' brains. Rachel Liddle reports

What is the story?
Women who are stressed during pregnancy may be at risk of reducing their child’s IQ, according to media reports.

UK research suggests that women who are stressed by domestic violence or rows with their partners in the months leading up to birth are more likely to have children with mental and behavioural problems.

High levels of cortisol produced by stressed mothers-to-be are believed to cross the placenta and enter the bloodstream of the baby. This can affect development of the child’s brain.

The latest study showed that babies exposed to the highest levels of cortisol in the womb had a lower than average IQ at 18 months than those whose mothers were not stressed.

Up to 15 per cent of the one million cases of attention-deficit hyperactivity disorder (ADHD), cognitive delay and anxiety among children in the UK could be due to maternal stress during pregnancy, say the papers.

What is the research?
The study was carried out by a team of researchers at Imperial College London looking at the long-term effects of antenatal stress on child development. The latest findings were presented at a conference of the Royal College of Psychiatrists last month.

It included earlier analysis of data from 7,363 participants in the Avon Longitudinal Study of Parents and Children.

This showed that children born to the most anxious 15 per cent of mothers-to-be were at twice the average risk of developing ADHD.

The latest study involved 125 infants whose mothers were re-cruited between 2001 and 2004 when undergoing amniocentesis.

Extra amniotic fluid and maternal blood samples were collected for analysis of hormones, including cortisol.

When the infants were 18 months old, they were assessed by researchers using the Bayley Scale, which gives a mental development index (MDI).

Children with no stressful events had an average score of 100, but this dropped to 95 for children whose mothers suffered three or more stressful events during pregnancy or one stressful event regarding their relationship with their partners.

Postnatal stressful events appeared to have a less powerful effect on MDI.

Emotional problems with a woman’s relationship and mental illness were the only areas that appeared to affect MDI.

What do researchers say?
Lead researcher Professor Vivette Glover, an expert in peri-natal psychobiology, said studies in rats and monkeys had demonstrated a link between antenatal, but not postnatal, stress and be-havioural problems in offspring.

The latest research supports the theory that this also occurs in humans. But follow-up examinations, including MRI scans of the brain, are needed when the children reach six years old, said Professor Glover. Maternal stress is one potentially modifiable factor in foetal neurodevelopment.

‘It depends on interactions with genetics, and later, upbringing,’ she added.

More now needs to be done to determine how maternal stress influences brain development in the human child, said Professor Glover: ‘Both the monkey and rat [studies] have shown that cortisol is the prime mediator from mother to foetus for neurodevelopment.’

The Imperial College team has already demonstrated a strong link between levels of maternal cortisol and that in the amniotic fluid surrounding human foetuses.

‘The final thing is that we’ve got an inverse link between amniotic cortisol and child development,’ said Professor Glover.

GPs should help pregnant women who are stressed to ease their problems, she added. ‘I don’t think the implication of this is increased prescribing, but any non-pharmacological intervention is worth a try.’

What do experts say?
Dr Somnath Banerjee, a community paediatrician in Kent, said that while stress in pregnancy can affect the child, he did not agree that high cortisol levels in the mother were necessarily to blame.

A woman’s blood levels of cortisol are always slightly higher than normal in pregnancy, he said. ‘If the mother is stressed during pregnancy, this is likely to lead to premature birth and low birth weight.’

Both factors increase the risk of a child having behavioural problems, said Dr Banerjee.

‘If she smoked cigarettes more or used alcohol because of stress, we know medically this child is more likely to develop ADHD,’ he added. ‘All these things are interrelated, so if you try to pinpoint any one thing, it is going to be difficult.’

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