A fallopian tube is one of two narrow, muscular tubes that connect the ovaries to the uterus. Each tube is roughly 10 cm (about 4 inches) long and 1 cm in diameter, and its primary job is to provide the space where egg and sperm meet. Fertilization doesn’t happen in the uterus, as many people assume. It happens inside the fallopian tube.
Anatomy of the Fallopian Tubes
Each fallopian tube has four distinct segments, each with a different width and role. Starting closest to the uterus and moving outward:
- Uterine (intramural) part: A tiny channel, only about 0.7 mm wide and 1 cm long, that passes through the muscular wall of the uterus itself.
- Isthmus: A firm, rounded section about 3 cm long and 1 to 5 mm wide. This is the narrowest segment you can see outside the uterus.
- Ampulla: The widest section at up to 1 cm across, stretching about 5 cm. Its inner surface is elaborately folded, creating a complex environment where fertilization typically takes place.
- Infundibulum: A trumpet-shaped opening at the far end, fringed with finger-like projections called fimbriae. Each fimbria is about 1 mm wide. They sweep across the surface of the ovary to catch a released egg and guide it into the tube.
The tube wall itself is built from three layers: an inner mucous lining, a middle layer of muscle, and an outer coating of smooth tissue. The inner lining is packed with two important cell types: cells that secrete nourishing fluid and cells covered in tiny hair-like projections called cilia. Both are essential for moving eggs, sperm, and embryos through the tube.
How the Tube Moves an Egg to the Uterus
When an ovary releases an egg (ovulation), the fimbriae at the end of the nearest fallopian tube sweep it inside. From there, the egg needs to travel the full length of the tube to reach the uterus, a journey that takes several days. Three forces work together to make this happen: rhythmic muscle contractions that squeeze the egg along, the constant beating of cilia that push it forward, and a flow of fluid secreted by the tube’s lining.
The tube doesn’t move things at a constant speed. The cilia beat at a higher frequency around the time of ovulation and slow down a few days later. This slowdown likely prevents an embryo from arriving in the uterus too early, before the uterine lining is ready for implantation. The timing is precise: the tube essentially holds the embryo until conditions are right.
How Hormones Control the Tubes
The fallopian tubes change dramatically across the menstrual cycle, driven by the same hormones that prepare the uterus for pregnancy. During the first half of the cycle, rising estrogen causes the cells lining the tube to grow taller and develop more cilia. Fluid secretion increases, creating a hospitable environment for sperm and egg. This is when the tube is most active and best equipped for fertilization.
After ovulation, progesterone levels climb and estrogen falls. The lining cells shrink, shed some of their cilia, and produce less fluid. That fluid also becomes thicker and more protein-rich. By the end of the cycle, when both hormones drop to their lowest levels, the lining returns to a flat, quiet state with very few cilia visible. The whole system essentially resets, then rebuilds again the following month.
Ectopic Pregnancy
An ectopic pregnancy occurs when a fertilized egg implants outside the uterus. About 90% of the time, this happens inside a fallopian tube. The uterus is the only organ designed to stretch and accommodate a growing fetus. Fallopian tubes cannot expand the same way, and as the embryo grows, it can rupture the tube.
A ruptured ectopic pregnancy causes sudden, sharp lower abdominal pain and can lead to severe internal bleeding, dangerously low blood pressure, fainting, and in some cases, death. Shoulder pain and rectal pressure are less obvious warning signs that can accompany a rupture. Ectopic pregnancy is a medical emergency, and a ruptured tube often needs to be surgically removed.
Tubal Blockage and Infertility
If one or both fallopian tubes are blocked or damaged, eggs and sperm can’t meet, and pregnancy through intercourse becomes difficult or impossible. This is called tubal factor infertility, and it has several common causes:
- Pelvic inflammatory disease (PID): Often the result of untreated sexually transmitted infections, particularly chlamydia and gonorrhea. PID can inflame and scar the tubes.
- Endometriosis: Tissue similar to the uterine lining grows outside the uterus, sometimes on or around the tubes, causing adhesions and blockages.
- Previous surgery: Abdominal or pelvic surgeries, including surgery for a previous ectopic pregnancy or even a ruptured appendix, can leave scar tissue that blocks the tubes.
- Tubal ligation: A deliberate sterilization procedure (“getting your tubes tied”) that blocks the mid-segment of the tube. Reversal surgery is not always successful, and mid-segment blockage can result.
How Doctors Check Tubal Health
The standard test for evaluating whether the fallopian tubes are open is a hysterosalpingogram, commonly called an HSG. It’s an X-ray procedure done in a radiology suite, and it takes about 15 to 30 minutes. You lie on a table as you would for a pelvic exam, a speculum is placed, and a thin catheter is threaded through the cervix. A contrast dye is slowly injected through the catheter into the uterus while X-ray images are taken in real time.
If the tubes are open, the dye flows through each one and spills out the fimbriae at the far end. If the dye hits a point where it stops, that indicates a blockage. Your provider may ask you to shift positions during the test so they can watch the dye from different angles. The procedure can cause cramping similar to menstrual pain, but it’s brief.
Fallopian Tubes and Ovarian Cancer Prevention
One of the more surprising developments in gynecologic medicine is the growing evidence that many ovarian cancers don’t actually start in the ovary. Researchers have found precancerous lesions in the fallopian tubes that closely resemble high-grade serous ovarian cancer, the most common and aggressive type. The current theory is that abnormal cells originate in the tube and then spread to the ovary secondarily.
This has led to a practice called opportunistic salpingectomy: removing the fallopian tubes during a pelvic surgery that’s already being done for another reason, such as a hysterectomy or sterilization. The Society of Gynecologic Oncology has recommended that surgeons consider this approach for women who have finished having children. Studies show that removing the tubes during a hysterectomy does not increase surgical complications, and it does not affect ovarian function. Hormone levels, egg reserves, and blood flow to the ovaries remain unchanged after the tubes are removed, based on follow-up data spanning three to five years.
Removing the tubes reduces ovarian cancer risk but does not eliminate it entirely, since some ovarian cancers arise through other pathways. Still, it represents a meaningful prevention strategy for a cancer that is notoriously difficult to detect early.