Women who suffer stress during pregnancy transmit their anxiety to their unborn child from as early as 17 weeks, research indicates.

Stress levels in foetuses only four months old — about the time the pregnancy starts to show — rise and fall in line with those of their mothers’.

The findings prompted calls for employers, family and friends to be aware of the risks and offer more help to moth-ers-to-be.

“For the first time, there’s solid evidence to show that an unborn child may be exposed to maternal stress as early as 17 weeks in development,” said Claire Friars, a midwife for Tommy’s, the baby charity.

“What is now clear is that high levels of stress in pregnancy can, in some cases, be detrimental to the health of the baby and to remain as stress-free as possible is certainly important. It is vital that pregnant women are given adequate support and reassurance from their family, friends and employers, to ensure they have a happy and healthy pregnancy.

A recent survey of 1,000 mothers-to-be conducted by Tommy’s found that pregnant women regularly felt stress at work. One in ten said that their employer was unsupportive when they announced their pregnancy and a quarter felt under pressure from employers who expected them to work just as they did before they became pregnant.

The research measured the stress hormone cortisol in the mother’s blood and in the amniotic fluid around the baby.

As the mother’s stress rose, so did that of the baby, according to Professor Vivette Glover at Imperial College London and consultant obstetrician Pampa Sarkar, of Wexham Park Hospital in Berkshire.

“We do not wish to unduly worry pregnant women. It should be remembered that one of the best ways for people to avoid general stress is to lead a healthy, balanced lifestyle,” Dr Sarker said.

“We are all a product of our developmental history. One of the times when we are most susceptible to the influences of our surrounding environment is when we are developing as a foetus in our mother’s womb. We found that the strength of this correlation became stronger with increasing gestational age. We now need to carry out further work to unravel the mechanisms by which maternal stress affects the foetus, both during foetal life and through into childhood.”

The theory behind the effect is that foetal programming is supposed to prepare babies for the life they will experience outside the womb. If the mother faced serious dangers, the baby had to be programmed to be born into a dangerous world. But these hangovers from the evolutionary past are no longer relevant, Professor Glover said.

The research is published in the May edition of Clinical Endocrinology. Professor Glover has previously shown a link between stress in pregnancy and the baby’s IQ. The greater the stress felt by the mother, measured by cortisol levels, the lower the IQ. The babies of stressed mothers were also more likely to be anxious and to show signs of attention-deficit disorder.

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