According to our data, a temporal association exists between the
uterine contraction and the reduction in placental oxygenation. At
the very beginning of the contraction, the placental oxygenation
remains unaffected. However, within approximately 30 s, the
placental oxygenation starts to decrease. During uterine relaxation,
the placental oxygenation slowly recovers, although oxygenation
does not fully recover until approximately one minute after the end
of contraction