Pregnant women who have chronic high blood pressure (hypertension) are much more likely to suffer from some sort of adverse pregnancy outcome, such as a premature delivery or even the death of their newborn, new research suggests.

According to UK scientists, chronic hypertension is estimated to cause complications in up to 5% of pregnancies.

Since health problems like obesity increase the risk of hypertension, and more and more women are now obese, the prevalence of chronic hypertension is expected to rise in the coming years.

The scientists decided to assess this health problem further. They analysed data from 55 studies carried out in 25 countries. They looked specifically at premature births, babies born with a low birth weight, admission rates to neonatal intensive care units and perinatal death.

Perinatal death refers to the death of a foetus after 20 weeks' gestation, including stillbirth, and the death of a newborn baby up to one month old.

The analysis revealed that all of these adverse outcomes were at least twice as likely to occur in pregnant women with chronic hypertension compared with pregnant women without the condition.

"Chronic hypertension is associated with a high incidence of adverse pregnancy outcomes compared with a general population," the scientists concluded.

Details of these findings are published in the British Medical Journal. In an accompanying editorial, experts from the University of Copenhagen in Denmark noted that very little research has been carried out on this condition.

"We still do not know the most effective, safe and cost-effective way to manage it and an urgent need remains for research to establish best clinical practice," they said.

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