Placental contractions in uncomplicated pregnancies

arXiv:2511.19547v1 Announce Type: new
Abstract: We first described the utero-placental pump phenomenon, in utero, in 2020. We have recruited 36 healthy pregnant women to undergo magnetic resonance imaging (MRI) between 29 and 42 weeks of pregnancy to further explore this occurrence in a single centre prospective observational study. Participants had fetal ultrasound to confirm normal growth. Dynamic MRI was acquired for between 15 and 32 minutes using respiratory triggered, multi-slice, single shot, gradient echo, echo planar imaging covering the whole uterus. All participants had a live birth of a healthy baby weighing over the 10th centile for gestational age and no conditions associated with placental dysfunction e.g. pre-eclampsia. There were no cases of severe maternal or fetal villous malperfusion on placental histopathology. Visible contractions were recorded for all participants who completed MRI scans. Contractions involving a decrease in placental volume >10% were classified as either placental or uterine by visual observation. Placental contractions occurred more frequently than uterine contractions (p=0.0061), were associated with a larger increase in the surface area of the uterine wall not covered by the placenta (p=0.0015), sphericity of the placenta(p