The placenta is only seen, and thus thought about, by most people, after birth. However, it is of course essential for normal fetal growth and development and maintenance of pregnancy. Furthermore, there is increasing evidence that placental dysfunction underlies the most significant diseases of pregnancy, including pre-eclampsia and fetal growth restriction (FGR). PE is the major cause of maternal death worldwide and FGR is a major contributor to perinatal morbidty and mortality. We hypothesised that understanding the placental phenotypes, associated with these diseases would enable improved understanding of their aetiologies and provide clues to new diagnostic tools and therapies.
Changes in placental size and shape and hormone production are associated with FGR. Furthermore, all the major determinants of the capacity of the placenta to supply nutrients and waste products are affected: (1) abnormalities in blood flow, probably related to failed transformation of the spiral arteries on the maternal side and structural and functional deficits in vessels of the fetoplacental circulation; (2) reduced surface area and increased thickness of the syncytiotrophoblast, the main cell layer in the placenta separating maternal and fetal blood; (3) altered activity of transporter proteins located to the maternal facing and fetal facing plasma membranes of the syncytiotrophoblast - decreased activity of some, but not all, with at least one transporter demonstrating an increased activity.
These placental characteristics may be used in early diagnosis of those pregnancies at risk of FGR, enabling focused care. Placenta Clinics are using this approach, integrating ultrasound assessment of blood flow and placental size and shape, with placental hormone measurements in maternal blood. However, more sophisticated techniques are required to detect in utero other characteristics of the FGR placenta described above, and we have focused on magnetic resonance imaging (MRI). Our data suggest that measurement of placental relaxation times, intravoxel incoherent motion, together with oxygen-enriched MRI measurements will provide useful tools for discriminating the phenotypes of the dysfunctional placenta.