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Pregnant mums sleeping on their back in late pregnancy can cut oxygen flow to an unborn child making stillbirths more likely, new combined University of Auckland and United Kingdom research has found.
“Sleep on side when baby’s inside,” is New Zealand’s official advice to women in late pregnancy.
In the latest study, women with healthy pregnancies underwent MRI scans at Auckland City Hospital lying on their backs and their sides. The scans showed the reduction in blood flowing to the uterus when mum lies on her back. On average, oxygen delivery to the fetus fell 6.2%, the paper just published in the Journal of Physiology showed.
This study quantifies the physical effects that seem to be linked to the heightened risk of stillbirth, the University of Auckland said in a statement.
``This helps us to answer questions about the rationale for the ‘sleep on your side’ advice,” said Sophie Couper, a University of Auckland medical school student who played a key role in the research. ``There’s still more to discover, but now we understand more about why sleeping on your back can be bad."
Healthy fetuses may be fine when their mothers sleep on their backs. But, for babies who are vulnerable, a mother’s sleeping position could be the extra factor that contributes to a stillbirth, the statement said.
The MRI scans showed reductions in blood and placental oxygen concentration when the women lay on their backs. On average, blood flow to the uterus decreased by 23.7%.
“It seems that sleeping in the wrong position is an additional stressor that may be too much for a fetus that is already vulnerable, resulting in an increased risk of a still birth,” said Professor Peter Stone, of the University of Auckland medical school. “Vulnerable fetuses include those which are smaller than usual and which may already be getting limited oxygen.”
Each year, in New Zealand, about 160 babies are stillborn in the last three weeks of pregnancy. A 10% decrease in late stillbirth might be achieved if all women followed the sleeping advice, according to the "Sleep on Side" website.
The study relied on collaboration with researchers at King’s College London and University College London.