A sweeping new map of the human placenta and uterus has revealed a cell type that scientists had never seen before — one that appears only during pregnancy and vanishes afterward.
Researchers at the University of California, San Francisco created what they describe as the most complete "atlas" of the maternal-fetal interface to date, tracking how tissues grow and change from five weeks of gestation all the way to birth. In the process, they stumbled on a subtype of cell that was entirely absent from the uterus outside of pregnancy but surged in number as the uterine lining transformed to support an embryo. "We asked around — no one knows what they are," senior author Jingjing Li told Live Science.
The mysterious cells appear to play a role in connecting the placenta to the mother's blood supply. Intriguingly, they carry receptors that respond to cannabinoids — both the body's own endocannabinoids and compounds found in cannabis, such as THC and CBD. That finding caught the researchers' attention because cannabis use during pregnancy has been linked to decreased placental blood flow, poor fetal oxygen delivery, and higher risks of preterm birth and low birth weight.
Li cautioned that these cells' cannabinoid sensitivity likely doesn't fully explain the dangers of cannabis use in pregnancy, noting that other mechanisms have been described in the medical literature. Still, the discovery adds an important new piece to the puzzle.
The study, published April 8 in the journal Nature, stands apart from earlier placental mapping efforts because of its scope. Previous studies examined only select windows of pregnancy, while this atlas incorporates tissue samples spanning nearly the entire gestational period, collected from tissue banks at UCSF and Stanford University. Beyond the newfound cell type, the atlas also identifies which cells are most likely affected in conditions like preeclampsia, potentially opening new avenues for diagnosing and treating pregnancy complications.