The fallopian tubes are slender, muscular channels connecting the ovaries to the uterus. Tubal factor infertility, the inability to conceive due to problems with these tubes, accounts for a significant portion of female infertility diagnoses. When the tubes become blocked or damaged, they physically interfere with the early stages of conception, making natural pregnancy improbable. Understanding their function reveals why obstruction leads to difficulties in achieving pregnancy.
The Essential Role of Fallopian Tubes in Conception
The healthy function of the fallopian tube involves actions that allow conception to take place. At the end of each tube, near the ovary, are finger-like projections called fimbriae, which sweep the surface of the ovary to capture the egg after it is released during ovulation. The tube is where the sperm and egg typically meet and fertilization occurs.
Once inside, the egg moves into the ampulla, the widest part of the tube, where it awaits the arrival of sperm. The inner lining is covered with thousands of microscopic, hair-like structures known as cilia. These cilia propel the fertilized egg, now a developing embryo, toward the uterus for implantation. This journey takes approximately three to five days, and interference with the cilia or muscular contractions disrupts this timing.
How Physical Obstruction Prevents Pregnancy
A physical blockage causes infertility by stopping reproductive components from reaching their destination. A complete blockage prevents sperm from reaching the egg for fertilization, or it stops the egg from entering the tube. Since the tube is an obligatory passage, natural conception cannot occur when both tubes are fully occluded.
If the blockage is only partial, it can still compromise the tube’s function, particularly the motile action of the cilia. Partial obstruction may allow sperm to pass through and fertilize the egg, but the resulting embryo is larger and cannot complete its journey to the uterus. The trapped embryo leads to complications.
A specific type of blockage is a hydrosalpinx, which occurs when the end of the tube is blocked and fills with fluid. This fluid is often inflammatory and toxic to an embryo and can leak back into the uterus. This backflow creates an environment hostile to implantation, reducing the chances of a successful pregnancy, even with assisted reproductive technologies like in vitro fertilization.
Common Reasons Blockages Occur
The most frequent cause of fallopian tube damage is Pelvic Inflammatory Disease (PID), often resulting from untreated sexually transmitted infections like chlamydia and gonorrhea. The infection leads to inflammation, and the body’s healing response creates scar tissue, or adhesions, inside and outside the tubes. This scarring effectively narrows or completely closes the tubal lumen.
Endometriosis is another major cause, where tissue similar to the uterine lining grows outside the uterus, including on the fallopian tubes. This misplaced tissue causes inflammation, leading to scar tissue formation or physically distorting the tube’s structure. The severity of the endometriosis often correlates with the degree of tubal damage and subsequent infertility.
Prior abdominal or pelvic surgeries, even those unrelated to the reproductive organs, can also introduce scar tissue that adheres to and blocks the tubes. Procedures like an appendectomy, certain C-sections, or surgery to remove ovarian cysts can cause adhesions to form. A tubal ligation is an intentional form of blockage. This surgical sterilization procedure closes the tubes to prevent pregnancy.
The Risk of Ectopic Pregnancy
A serious health risk associated with compromised fallopian tube function is an ectopic pregnancy, where a fertilized egg implants outside the main cavity of the uterus. Over 95% of ectopic pregnancies occur when the embryo implants within the fallopian tube itself. This typically happens because the tube is damaged or partially blocked due to prior inflammation or infection.
The damage may not prevent fertilization but is severe enough to impair the cilia’s ability to transport the embryo to the uterus. The embryo then implants prematurely into the tube wall and begins to grow. Since the fallopian tube is not designed to support a growing pregnancy, this condition is life-threatening. It can cause the tube to rupture, leading to severe internal bleeding, requiring early detection and treatment.