The placenta was known in Ancient times. We are likely familiar with the image of the Pharoah in ancient Egypt with his attendants carrying placentas with umbilical cords attached atop long stakes in a ceremonial procession. The placenta was thought to be the seat of the soul of the fetus and at least those of the wealthy were revered. Aristotle, in the third century BC, recognised the nutritive function of the placenta. The Japanese and Chinese also revered the placenta and umbilical cord and those of important people were often buried near shrines in their honour.
In the late 1960s and 1970s Robertson and Brosens established the placental bed biopsy and described the physiological changes in the spiral arterioles that occur in normal pregnancy and their failure to occur in preeclampsia. In the 1980s this was also shown for miscarriage, small for gestational age, preterm birth and stillbirth.
It also became clear that placental structural development was perturbed in women with pregnancy complications where utero-placental insufficiency is a feature. Then in the 1990s convincing evidence emerged that for most of the first trimester the placenta and embryo/fetus develop in a hypoxic environment as maternal blood flow into the placenta does not commence until about 10 weeks of gestation. It is thought that impaired remodelling of the spiral arterioles results in premature maternal blood flow into the intervillous space and oxidative damage that the early placenta is ill-equipped to counteract.
We now live in exciting times for placenta research. NIH has invested over $50million in the Human Placenta Project. Technological innovations in recent years are enabling unprecedented acquisition of data. Placental differentiation, growth and function are being explored using state of the art cellular, molecular and imaging modalities. Non-invasive screening of the placenta in real time is becoming a reality and will be increasingly used to identify and monitor pregnancies at risk.