Last updated at 13:16 12 June 2007

Women should keep out of the hot sun throughout pregnancy, according to experts.

The warning, from the Royal College of Obstetricians and Gynaecologists, comes amid predictions that Britain will see sweltering temperatures this summer.

It said the advice was particularly relevant to those in early pregnancy as babies develop most rapidly in the first three months after conception.

It also said that pregnant women are more sensitive to high temperatures, which can make them feel unwell.

Several studies have suggested that babies can be affected by heat during the first 12 weeks of pregnancy.

A study published in the British Journal of Obstetrics and Gynaecology in 2005 found that exposure to high temperatures in the first three months could lead to babies being born with a slightly lower birth weight.

Such babies are prone to a low IQ and learning disabilities. They are also more likely to exhibit behavioural problems at school.

The researchers, from the University of Bristol, concluded that an "increasing occurrence of temperature extremes - in particular heatwaves - could have important public health implications".

A spokesman for the royal college said yesterday: "Women in their first stages of pregnancy in the summer should be aware of the health risk surrounding increases in temperature.

"Pregnant women should stay out of the sun, wear loose clothing, keep well hydrated and eat healthy food little and often."

Sue Jacob, from the Royal College of Midwives, said getting hot causes the mother's blood vessels to contract as she tries to cool herself down - reducing the amount of nutrients that pass through into the foetus.

She added: "There is a tendency in Britain to rush out whenever the weather is nice but people should be aware of the hidden dangers too.

"Women should also take care during late pregnancy. High temperatures have been shown to lead to premature labour and an increased rate of miscarriage."

The college stressed that women should not panic but said they should take steps to protect themselves and their unborn babies.

These included dressing appropriately in hot weather by wearing a hat and light, loose clothes made from a natural fibre such as cotton.

Pregnant women should also stay in the shade between 11am and 3pm when the sun is at its hottest.

To cope with a heatwave, expectant mothers are also advised to eat more light meals, such as salads, and plenty of fruit and vegetables.

They should also avoid strenuous exercise which can raise the body temperature even further. Light to moderate exercise is okay.

Mothers-to-be should also avoid tea, coffee and alcohol, which can all increase the risk of dehydration.

The college said signs of heat exhaustion to look out for included increased body temperature, tiredness, light-headedness, and a dry mouth and throat.