Unexpected contractions discovered in utero

Functions of the human placenta in utero, including patterns of maternal blood flow in the intervillous space (IVS), remain largely unknown. A new study in PLoS Biology offers important new insights into various placental functions and describes a new physiological phenomenon.

Researchers from the University of Nottingham discovered unexpected contractions in utero by using magnetic resonance imaging (MRI) to examine the movement and oxygenation of blood in the human placenta.¹

For this investigation, they included 34 women with healthy pregnancies as the control group (HC), and 13 women with pregnancies compromised by preeclampsia as a model for altered placental function (PE).

When analyzing placentas in utero in the HCs, researchers found that the velocity of blood flow decreased as it moved through the uterine wall to the placenta. They also observed relatively fast flow in and out of the placenta, which further emphasizes the importance of venous outflow in the IVS.

In the PE pregnancies, researchers observed higher resistance to blood flow, which led to faster flow through the IVS. This led to a higher rate of percolation of blood flow in the placenta, thus altered patterns of blood movement.

The findings suggest that this pattern of percolation resulted in lower and much more variable oxygenation across placentas.

During this investigation, researchers witnessed unexpected contractions in which the placenta and underlying uterine wall contracted independent of the rest of the uterus. This process, deemed the “utero-placental pump,” led to transient reductions in placental volume and facilitated better blood flow through the placenta and fetus while expelling maternal blood.

Researchers observed these “utero-placental pump” contractions over a 10-minute period in 12 of 34 HP patients and in 7 of 10 PE patients. These contractions consisted of a reduction in the area and thickening of the myometrium beneath the placenta; stretching or expansion of the rest of the uterine wall; and a simultaneous reduction in placental volume by up to 40%.

Although these contractions varied in strength and duration, all caused the placenta to become thicker and appear darker and more heterogeneous.

The researchers did not find any differences in HP and PE contractions, but note that longer scanning and monitoring times would allow for confirmation.

The results of this study, according to the authors, could be used to improve placental models and optimize MRI protocols to identify placental abnormalities in pregnancy.

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Image Credit: Penny Gowland

Reference

1. Dellschaft Neele, Hutchinson G, Shah S, et al. The haemodynamics of the human placenta. PLOS Biology. bioRxiv 2020.02.07.938589; doi: https://doi.org/10.1101/2020.02.07.938589