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Friday, 19 November, 1999, 22:56 GMT
The key to a successful pregnancy
Small babies are at greater risk of developing high blood pressure

The way the placenta works may be a more important factor in determining the development of a foetus than any lifestyle a woman adopts while pregnant.

Babies with low birth weight have been shown to have higher levels of blood pressure and a higher risk of heart disease as children, adolescents and adults.

Scientists believe poor diet and smoking during pregnancy are likely to cause these problems, and children from lower socio-economic classes are most at risk.

But two research studies, published in the British Medical Journal, conclude the most important factor in giving birth to a healthy child is a placenta which works effectively to provide the growing foetus with the correct nutrients.

The two studies examined whether the link between birth weight and blood pressure is due to maternal factors, by examining the birth weights and subsequent blood pressure levels of twins.

One twin is usually heavier than the other and, unlike separate singleton pregnancies, twins experience exactly the same maternal factors during pregnancy.

Major study

Smoking has been linked to developmental problems
Professor Terence Dwyer and colleagues from the Menzies Centre for Population Health at the University of Tasmania studied 888 children until the age of eight years, including 55 pairs of twins.

Among the twins, they found the child with the lowest birth weight was likely to have the highest blood pressure.

As both twins shared the same mother the researchers concluded maternal factors could not be wholly responsible for birth weight and cardiovascular disease in later life.

They also found the same relationship in identical twins from the same egg, and thus concluded that genetic factors are also unlikely to be responsible for the association.

They believe the link between restricted growth in the uterus and later high blood pressure is more likely to be due to placental factors than to maternal nutrition.

Lower blood pressure

Similar findings were reported in a separate study of 492 pairs of female twins by Dr Neil Poulter, of Imperial College School of Medicine and a team from Guy's and St Thomas's Hospital Trust in London.

They also found that twins who were heavier at birth had lower blood pressure as adults.

Dr Poulter told BBC News Online the only factor that was different for twins was how nutrients reached them once they had been taken in by the mother.

"That must be some function of the placenta, " he said.

But he warned that it was still important that pregnant women ate a healthy diet and did not smoke.

He said: "This data does not in any way undermine the importance of the standard risk factors for disease.

"I went to rural Africa and although many of the babies were tiny there were no cases of diabetes, heart attack or stroke because their mothers did not smoke and did not have fat in their diet."

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