Can Blocked Tubes Cause a False Negative Pregnancy Test?
- A woman has two fallopian tubes, one on either side of her body. Each of the fallopian tubes connects to an ovary. Fertilization of the egg occurs within the fallopian tubes through which the egg travels from the ovary to the uterus. Fallopian tubes can become blocked for several reasons. Pelvic inflammatory disease (PID) causes scar tissue, which can block fallopian tubes, to build up on the walls of the tubes. Sexually transmitted diseases are a common cause of scarring that blocks tubes. Previous abdominal or pelvic surgery, such as a ruptured appendix can cause scarring as well. A condition known as endometriosis can also damage tubes and cause a build up of tubal scar tissue. In some women the structure of the tubes is abnormal, usually the result of a birth defect.
- In some cases, a fallopian tube may be only partially blocked, increasing the risk for a tubal or ectopic pregnancy. Because the fertilized egg is unable to reach the uterus to implant itself, it begins to develop in an area outside of the womb. According to the American Society for Reproductive Medicine, inside a fallopian tube is the most common site for at least 90 percent of all ectopic pregnancies. An ectopic pregnancy must be ended, as it cannot be carried to term. If not detected early, the ectopic poses the risk of rupture that would require emergency surgery to save a woman's life.
- Pregnancy tests are designed to detect human chorionic gonadotropin (hCG).The presence of this hormone appears in a woman's urine or bloodabout two weeks following conception, giving a positive pregnancy result. The placenta usually begins to produce hCG within 7 to 14 days after fertilization of the egg occurs. The hormone is produced whether or not the embryo attaches to the lining of the uterine wall. During a normal pregnancy, the levels continue to rise rapidly throughout the first three months. However, in the case of an ectopic pregnancy due to a blocked fallopian tube, hCG levels will be lower than normal. Low or decreasing quantitative serum levels suggest ectopic or nonviable pregnancy. Some women with ectopic pregnancies may have undetectable hCG levels if they wait too long to be tested. Levels of the hormone tend to peak at 10 to 12 weeks, after which time they begin to decline. This can cause a false negative urine pregnancy result.