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 Friday, 5 February, 1999, 12:39 GMT
Oxygen link to miscarriages
Ultrasound tests suggest oxygen levels are low in early pregnancy
Too much oxygen may be a significant cause of miscarriage in early pregnancy, say scientists.

One in four pregnancies ends in miscarriage and 15% of miscarriages occur between eight and 12 weeks after conception.

Half of early miscarriages are thought to be due to abnormalities in the foetus, but little is known about what causes the other 50% or about late and recurrent miscarriages.

Researchers at Cambridge University say they believe a major reason for early miscarriages could be that foetuses receive too much oxygen at a time when they are not developed enough to withstand it.

Toxic effects

They think there are two stages to pregnancy and that in the first stage the oxygen supply to the foetus is deliberately restricted.

Women who miscarry in the first three months may pass to the second stage too quickly.

Dr Graham Burton, who is leading the research, said: "Oxygen can be quite toxic. It contains free radicals which cause premature ageing.

"It may well be that during the period of early development in the womb the tissue is particularly susceptible to the toxic effects of oxygen and that too much oxygen kills it.

"Research on animals shows that a higher level of congenital abnormalities may be linked to high levels of oxygen. It may be we are protecting ourselves by keeping oxygen levels low in the early stages."

The scientists have come to their hypothesis after 18 months of studying normal pregnancies.

The researchers, funded by the Medical Research Council, used new imaging techniques to study the supply of oxygen to the foetus.

They found that there were two clear stages to pregnancy - the first three months and the last six months and that oxygen levels changed after three months.


Dr Graham Burton, who led the research, said: "It became increasingly clear that a switch does occur. Previously pregnancy was thought of as a continuum.

"It was logical to go from this hypothesis to one which said that over-supply of oxgyen might cause miscarriage."

The hypothesis will be tested out over the next two years, using funds from a 73,000 grant from the charity Tommy's Campaign.

The researchers will study women in the process of miscarrying and those threatening to miscarry as well as the placenta of women who have miscarried.

Vivienne Creevey, chief executive of Tommy's Campaign, said: "At whatever stage of pregnancy a miscarriage occurs, it is a very real and devastating loss for parents.

"We believe this project will help shed light on this traumatic and potentially avoidable problem."

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