The biological connection between a pregnant woman and her developing baby—the human maternal–fetal interface—is a specialized, transient organ composed of uterine cells from the mother and fetal cells that acts as a barrier, supports fetal growth, and maintains the mother’s health. The cellular complexity of the maternal-fetal interface has limited scientists’ ability to study how healthy pregnancies develop and why complications arise. The underlying cellular, molecular, and spatial programs of the interface—which forms about a week after fertilization and lasts until birth—has remain incompletely defined.

Now, the human maternal–fetal interface has been mapped in unprecedented detail by scientists at the University of California, San Francisco (UCSF), revealing new cell types and providing insights into conditions such as preeclampsia, preterm birth, and miscarriage.

“By examining this tissue cell by cell across pregnancy, we can begin to understand both normal development and what may go wrong,” said Susan J. Fisher, PhD, professor of obstetrics, gynecology, and reproductive sciences at UCSF.

The team generated a comprehensive atlas of the human maternal–fetal interface across normal pregnancies, from early gestation to term. The researchers did this by “integrating large-scale paired single-nucleus transcriptomic and chromatin accessibility profiling with submicrometer-resolution spatial transcriptomics and CODEX multiplex protein imaging.”

Using these tools, the researchers analyzed about 200,000 individual cells and compared them with nearly one million cells in their original positions within the uterine and placental tissue. This enabled them to identify different cell types, track how they develop, and see how they are linked to pregnancy complications.

“This work gives us a much clearer picture of this critical region than ever before,” said Jingjing Li, PhD, associate professor in UCSF’s Department of Neurology and the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research.

This work is published in Nature in the paper, “Single-Cell Spatiotemporal Dissection of the Human Maternal–Fetal Interface.”

The atlas revealed a previously unknown maternal cell type located where fetal placental cells first enter the uterus. These cells appear to regulate how deeply placental cells invade uterine tissue, a process that is essential for establishing blood flow to the fetus. The researchers found that these cells carry a cannabinoid receptor, and exposure to cannabinoid molecules caused them to further restrict placental cell invasion.

“Population studies have linked cannabis use during pregnancy to poorer outcomes,” said Cheng Wang, PhD, a postdoctoral fellow at UCSF. “This cell type may help explain the biological basis of that association.”

To understand how complications arise, the team integrated genetic data from more than 10,000 patients. They mapped genetic risk signals for conditions including preterm birth, preeclampsia, and miscarriage onto regulatory regions of DNA that control gene activity. This approach allowed the researchers to identify the specific cell types and states most strongly associated with each condition.

The team then focused on preeclampsia, a potentially life-threatening disorder marked by sudden high blood pressure. They found that the most affected cell types are involved in remodeling the mother’s uterine blood vessels, a process required to supply adequate blood to the placenta. The findings suggest that preeclampsia may result from disrupted communication between maternal and fetal cells that normally coordinate this process.

Having established a detailed map of healthy pregnancies, the researchers plan to study complicated pregnancies to identify potential targets for treatment.

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