WASHINGTON — In a groundbreaking study using mice, researchers have employed optical coherence tomography (OCT) to gain unprecedented insights into the transport mechanisms of preimplantation embryos within the fallopian tube. This discovery could pave the way for a deeper understanding of infertility and pregnancy complications in humans.
The fallopian tube, or oviduct, is a crucial component of the female reproductive system, linking the ovaries to the uterus. It plays a vital role in several reproductive processes, including the transportation of eggs and sperm, facilitating fertilization, and moving 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,” stated Shang Wang, the research team leader 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.”
Advanced Imaging Techniques Reveal New Mechanisms
Published in the Biomedical Optics Express journal by the Optica Publishing Group, the study utilized advanced OCT imaging to observe the dynamics of the oviduct with an embryo inside. The research unveiled a previously unknown pumping mechanism that propels 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,” explained Huan Han, a doctoral candidate in 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
Wang’s laboratory focuses on developing imaging techniques to study the biomechanics of reproductive and developmental processes within the oviduct. “Little is known in this critical area, due to the technical difficulty in studying it,” Wang noted. “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, researchers used an implantable window to bypass the mouse’s skin and muscle, providing direct optical access. They measured the cilia beat frequency by analyzing fluctuations in the OCT intensity signal and assessed the oviduct’s muscular activity through 4D OCT imaging, measuring the cross-sectional luminal area. This provided insights into how contraction waves propagated through the oviduct.
The Leaky Peristaltic Pump Mechanism
The study initially focused on the isthmus, the section of the oviduct closer to the uterus. However, it was only when both the ampulla and the isthmus were imaged together using 4D OCT that researchers discovered contraction waves originating in the ampulla and moving through the isthmus, facilitating embryo movement.
“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,” Wang explained.
This mechanism allows for a bidirectional movement that ultimately transports the embryo toward the uterus. The constricted lumen at the oviduct’s turning points can stop backward embryo movement, resulting in a net displacement toward the uterus.
Implications for Future Research
Although the imaging methods have been used previously, this study marks the first time they have been applied to understand embryo transport in the mouse model. “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,” Wang added.
Building on this work, the researchers plan to conduct imaging studies to understand abnormal transport scenarios, such as when embryos remain inside the oviduct, potentially leading to tubal ectopic pregnancies.
This pioneering research not only opens new avenues for understanding reproductive biology but also holds promise for developing clinical interventions to address infertility and pregnancy complications.
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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