WASHINGTON — In a new mouse study, researchers have used optical coherence tomography (OCT) to uncover new insights into how the fallopian tube transports preimplantation embryos toward the uterus for pregnancy. These findings help lay the foundation for understanding certain causes of infertility and pregnancy complications in people.
The fallopian tube, also known as the oviduct, is a tubular structure that connects the ovary and the uterus. It is responsible for several critical processes that lead to pregnancy, including transporting eggs and sperm, hosting fertilization and transporting preimplantation embryos as they develop.
"Most of the oviduct's functions — including moving early embryos toward the uterus — haven't been observed in their natural environment, and we don't yet know what biological mechanisms ensure they work properly," said research team leader Shang Wang from Stevens Institute of Technology . "This lack of information is a key reason why the causes of tubal ectopic pregnancy and oviduct-related infertility remain largely unknown."
In the Optica Publishing Group journal Biomedical Optics Express , the researchers report results from using advanced OCT imaging approaches to capture the oviduct dynamics with the preimplantation embryo inside. This mouse study revealed that the oviduct uses a previously unknown pumping mechanism to drive embryo movement during preimplantation development.
"OCT was ideal for this study because it provided label-free 3D imaging at a scale that resolved structural details throughout the oviduct's inner space while capturing images fast enough to visualize tissue and cell dynamics," said Huan Han, a doctoral candidate in Shang Wang's laboratory. "This research is just the beginning of uncovering how the oviduct supports pregnancy and early embryo development, which could ultimately lead to better strategies for clinical care of ectopic pregnancy and certain forms of infertility."
Peering into the oviduct
One of the focuses in Wang's lab is on developing imaging techniques to study the biomechanics of reproductive and developmental processes that occur in the oviduct. "Little is known in this critical area, due to the technical difficulty in studying it," said Wang. "We applied advanced OCT-based in vivo imaging methods in the mouse model, opening a unique window into the embryo movement and the early stage of embryo development inside the fallopian tube."
To visualize processes in the mouse oviduct, the researchers used an implantable window to bypass the mouse's skin and muscle, providing direct optical access to the area. Since the motile hair-like cilia that line the oviduct's luminal surface are too small to be captured with OCT, they measured the cilia beat frequency by analyzing fluctuations in the OCT intensity signal. They also assessed the oviduct's muscular activity by performing 4D (3D+time) OCT imaging of the oviduct and measuring the cross-sectional luminal area. This also provided information on how contraction waves propagated through the oviduct.
The oviduct has two main parts: the ampulla, where fertilization occurs, and the isthmus, closer to the uterus, where embryos develop and move bidirectionally during preimplantation. To investigate the pumping mechanism underlying this bidirectional embryo movement, the researchers initially only focused on the isthmus for imaging and analysis, which did not reveal how the movement took place.
Leaky peristaltic pump
Suspecting a broader mechanism, the researchers then used 4D OCT to image both the ampulla and the isthmus. This revealed contraction waves that originated in the ampulla and propagated through the isthmus, along with relaxation and embryo movement. Quantitative spatiotemporal analysis of this full view uncovered how the oviduct drives bidirectional movement to transport the embryo toward the uterus.
The ability to image and analyze both oviduct regions together revealed that the oviduct operates as a leaky peristaltic pump — contraction wave pushing fluid forward and relaxation at earlier contraction sites pulling fluid back — when transporting the preimplantation embryo in the isthmus. The researchers also found that constricted lumen at the oviduct turning points can stop the backward embryo movement at times, producing net displacement of embryos in the isthmus toward the uterus.
"Although the advanced imaging methods we used have been demonstrated and reported previously, this is the first time they have been applied to study how the oviduct transports preimplantation embryos in the mouse model," said Wang. "Now that we understand the normal process of how the embryos are transported, it is possible to investigate the abnormal processes underlying related disorders and diseases."
Building on this work, the researchers plan to perform imaging studies to understand abnormal transport that occurs when embryos remain inside the oviduct, which can lead to a tubal ectopic pregnancy.
Paper: H. Han, T. Fang, A. Mukhamedjanova, S. Wang, "In vivo dynamic imaging reveals the oviduct as a leaky peristaltic pump in transporting preimplantation embryo toward pregnancy," Biomed. Opt. Express, 7, (2025).
DOI: 10.1364/BOE.565065
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About Biomedical Optics Express
