Female sterilisation is a method of contraception that involves the fallopian tubes, which link the ovaries to the uterus, being blocked or sealed. As a result, a woman's eggs should be prevented from reaching sperm, thus preventing the likelihood of an egg becoming sterilised.

These eggs, which will continue to be released from the ovaries as before, are then naturally absorbed into the woman's body. Sterilisation is usually performed under general anaesthetic, although depending on the method used, can also be carried out under local anaesthetic.

The vast majority of procedures are effective; however, there is always a risk that the operation will not go to plan and this can lead to unwanted pregnancy.

• The sterilisation could fail and the fallopian tubes could rejoin, making you fertile again
• When the tubes are blocked, there is a small risk of complications, which can include infection and internal bleeding
• If a pregnancy does occur after the operation, there is a greater risk of it being ectopic, which involves the growth of the fertilised egg outside of the womb

Female sterilisation is not a foolproof method of contraception and all women undergoing the procedure should be warned of possible failure.

In the past, many sterilisations were performed via a laparotomy (opening of the abdomen) and the most popular and successful was the Pomeroy technique. This involved drawing the tube up into a loop and then tying off the base with catgut. The loop was then cut off. This method is still sometimes carried out using a laparoscope and is usually highly effective.

Nowadays, the vast majority of sterilisations are performed using laparoscopy (keyhole surgery). The most common laparoscopic techniques include:

• Application of clips (otherwise known as Hulka-Clemens or Filshie techniques)
• Application of silastic rings (otherwise known as falope rings)
• Using heat to cut the tubes (diathermy coagulation). This method, however, is becoming less common due to a high failure rate

Surgical mistakes are more likely to occur with the closed laparoscopic method than with the abdomen open at laparotomy, particularly in the hands of an inexperienced surgeon, and it is not uncommon for the round ligaments in the pelvis to be mistaken for the fallopian tubes.

When clips are used, it is important that they are applied to the narrowest part of the tube (the isthmus). If they are applied to the wider part, they may not completely occlude the tube. Most surgeons now apply two clips to each tube in an attempt to reduce failure rates

Regardless of the method of sterilisation used, and however expertly it is performed, operations can still sometimes fail. The two main reasons for this are

• The two halves of the divided fallopian tube can come together and rejoin (recanalisation)
• The formation of a fistula (an abnormal passage) between the tube and the peritoneum (lining of the abdominal cavity). This happens most commonly with diathermy coagulation

Female sterilisation is not a fool proof method of contraception and all women undergoing the procedure should be warned of possible failure.

In cases where a woman becomes pregnant shortly after the operation (in less than 12 months), it has been suggested that this is more likely to be due to surgical error than simply luck.