The egg travels from the ovary to the uterus through the fallopian tube. If the tubes are damaged they can become blocked so the sperm is prevented from reaching the egg and fertilising it. Blocked tubes can be caused by pelvic inflammatory disease, sexually transmitted diseases such as chlamydia, and previous sterilisation surgery.
Symptoms: there are no symptoms.
Diagnosis: a Hycosy diagnostic test is where a dye is inserted into the tubes and followed using an ultrasound scan. If the dye travels through the tubes to the uterus then tubal patency is confirmed and the tubes are clear. This test can be performed at any time of the cycle assuming the couple have not had unprotected sex.
Possible treatment: in a small minority of cases laparoscopic surgery can be used to open tubes, but more often IVF is recommended as the eggs are generally unaffected.