By Michael Holden
LONDON, Jul 06 (Reuters) - Oxygen may be essential for life but a sudden
rush during the early weeks of pregnancy could spell death for a foetus, British
scientists said on Wednesday.
Their study found that the amount of oxygen foetuses receive tripled between
the eighth and 15th week of pregnancy, and that this could account for a
significant number of miscarriages.
One in six pregnancies ends prematurely, and obstetricians called for more
tests to see whether high doses of antioxidants could help cut the risk of
miscarriage.
"People have known for a number of years that this period of pregnancy is a
vulnerable one and I think we are finally able to give a clue as to why that is
the case," Graham Burton, of Cambridge University, told Reuters.
Burton and his colleague Eric Jauniaux, of University College London, placed
a tiny monitor in the placentas of 30 women and studied the oxygen levels during
their first three months of pregnancy.
Most embryologists have traditionally thought that oxygen levels gradually
increase during pregnancy.
But Burton and Jauniaux's research found that oxygen levels in the blood
flowing through the umbilical cord tripled between the eighth and 15th week of
pregnancy.
"There is in fact very little blood flow to the placenta before about 10
weeks of pregnancy, and in cases which are about to miscarry then there is an
excessive and early onset of maternal blood flow," Burton said.
"We know that these tissues are very susceptible to oxygen and the high
levels of oxygen associated with that blood flow cause the tissues to degenerate
and hence to miscarry.
"There's a wide spectrum of conditions associated with miscarriage, and I
wouldn't say necessarily this causes all, but I think it may be associated with
a significant number."
The research suggested that cells called cytotrophoblasts, which anchor the
placenta in the womb and invade the blood vessels to limit oxygen intake,
dissipate at about eight to 10 weeks, allowing more of the gas in.
A diet rich in antioxidant vitamins such as vitamins C and E could help
protect the foetus from this sudden change in their environment, Burton said.
"You can imagine that any additional stresses such as alcohol or cigarette
smoking which are associated with miscarriage might exacerbate that stress, and
we may be able to tilt the balance backwards by giving antioxidants which are
part of a normal healthy diet anyway."
