During the contraction, the area of the placenta assessed by the
number of pixels within the placenta ROIs was also significantly
reduced. In average, the number of pixels was reduced 17 ± 7%,
which was clearly visible in the MR images (Video1). As the area
was reduced in three separate slices, this finding indicated a loss in
placenta volume. As opposed to the changes in placental BOLD
signal, the placental area was regained immediately at the end of
uterine contraction (8 ± 27 s, Fig. 3).
None of the women reported uterine contractions during the
MRI acquisitions.