The blockage in the Fallopian tube can prevent a sperm from reaching an egg released from the ovary at ovulation or the fertilised egg reaching the uterus. At least one tube must be clear to allow the sperm to fertilize an egg and the resulting embryo to be transported to the uterus.

According to the American Society for Reproductive Medicine (ASRM), 25 to 35 percent of female infertility cases are caused by problems with the fallopian tubes.

Tubal damage is particularly suspect in women with regular, ovulatory menstrual cycles and a partner with normal sperm.

Cause
  There are some causes of blocked fallopian tubes like endometriosis, by infection following pelvic inflammatory disease or from pelvic surgery(ruptured appendicitis, previous tubal ligation surgeries ) and also even in whom tubes are absent congenitally.
  It may also increase the risk of ectopic pregnancy where the fertilised egg implants in the fallopian tube rather than in the uterus in patients with blocked damage fallopian tubes.
  Tubal blocks can be proximal, mid-segment or distals. A blocked distal tube frequently dilates and accumulates toxic fluid (hydrosalpinx).
  Chronic Pelvic infection ( tuberculosis , STDs)

Ways to diagnose blocked fallopian tubes:
  Ultrasonography(2D/3D)
  Hysterosalpingography (HSG)
  Saline/Dye infused Sonohysterosalpingography(SIS)
  Laparoscopy is only the gold standard method as compared to above.

Surgeries for the blocked tubes:
  If an imaging test has shown that a woman has a proximal tubal blockage, a tubal cannulation may be performed. This will only be successful if the blockage is due to spasm or a mucous plug. Cannulation cannot resolve proximal tubal scarring.
  A laparoscopic procedure known as a fimbrioplasty attempts to repair scarred fimbria. A fimbrioplasty should only be considered for minimal distal tubal blockage.
  Removing the fallopian tube entirely because of the damage or disease is referred to as a salpingectomy. This may be used to treat hydrosalpinx.
  A salpingostomy can save the fallopian tube, while surgically creating a new opening in the tube. This is often used to remove an ectopic pregnancy.
  Disadvantage of surgery: Damage to the fallopian tube usually results in damage to the cilia. While surgery can open some blockages of the fallopian tubes, it cannot repair the cilia. For this reason, surgical repair can only be considered if the damage to the tube is minor. Severe proximal and distal tubal blocks are better treated with invitro fertilization.