Scientists from the University of California, San Francisco (UCSF) have discovered a new type of cell that appears to be unique to pregnancy. These cells, which are not present in the uterus outside pregnancy, rise in number at the start of gestation as the uterine lining grows to support the embryo. They appear to be involved in linking the placenta to the maternal blood supply and carry receptors that respond to cannabinoids, including body-made chemicals and cannabis compounds. The discovery may explain why cannabis use in pregnancy is linked to health consequences such as decreased blood flow to the placa, poor oxygen delivery to the fetus, and a heightened risk of preterm birth, low birth weight and NICU admission. The researchers used data from about 1.2 million placental and uterine cells, including 200,000 isolated cells and 1 million cells embedded in their original locations within the tissue. The new atlas also revealed links between a given cell's gene activity and its behavior, which could potentially develop treatments for high-risk conditions.