Most women who are sterilised are delighted with their choice of contraception. It's a very reliable operation and must be seen as a permanent method of preventing pregnancy (in other words you shouldn't consider it if you think there’s a chance you may change your mind in the future). However, there's a very small failure rate.

Low failure rate

Pregnancy rates for contraceptives are measured in terms of the number of pregnancies which occur for every 100 years of use of that method by a woman. (A bit of statistical wrangling goes on here because clearly one woman on her own isn't going to use a contraceptive for 100 years! Another way of looking at the figure is the number of pregnancies which occur when 100 women use the method for one year.)

With female sterilisation, the failure rate is 0.05 pregnancies for every 100 women-years of use This means that if 2,000 women choose sterilisation, one will become pregnant within a year. But some experts report failure rates within a woman's lifetime as much as ten times this. The longest follow-up study of the most popular method for female sterilisation (where the fallopian tubes are clipped: see below) showed that for every 1,000 operations, two to three women became pregnant within the next ten years.

Despite these failures it's the most effective contraceptive method and compares to 0.5 pregnancies per 100 women-years for the contraceptive pill, 2.5 pregnancies per 100 years for barrier methods such as the condom or diaphragm and 80 pregnancies per 100 years when no contraception is used.

(These are all general figures - individual rates depend on many factors such as age of the woman and how carefully she uses the contraceptive method.)

One problem is that if pregnancy does occur there's an increased risk of an ectopic pregnancy.

Chances of reversal

Although female sterilisation should be considered permanent, these days surgical techniques to reverse a sterilisation are very good. Up to 75 per cent of women who undergo reversal surgery do eventually get pregnant, although a woman's chances depend on her own individual factors such as how the original sterilisation was done, age, and so on.

Techniques for sterilisation

Most female sterilisations are done under general anaesthetic using a technique called laparoscopy (a few are done this way under local anaesthetic). A long telescopic tube called an endoscope is passed through the skin and into the area around the fallopian tubes. Operating instruments can be passed through the endoscope, allowing the surgeon to operate on the fallopian tubes.

The aim is to permanently block the fallopian tubes so that eggs are unable to pass from the ovary into the womb and meet the sperm. The fallopian tubes may be blocked in several ways:

• by cutting out a small section and tying off the cut ends
• by putting a tight band around the tubes and constricting them to squash the inner passage
• by putting plastic clips rather like crocodile clips across each tube to squash and block it (the most effective and most easily reversed technique)
• by electrically cauterising (that is, burning and cutting each fallopian tube) and sealing the ends

The operation may be done as a day case or you may need to stay in overnight. It may be quite painful afterwards but most women recover very quickly and are back at work in three to four days.

Another common technique, especially for women who are rather overweight or who have previous pelvic surgery, is to operate through a small cut just below the tummy button. This is known as a mini-laparotomy. Alternatively, if a woman has other problems such as very heavy periods, a hysterectomy may be suggested. This may be done through a larger cut, or by operating through the vagina.

This article was last medically reviewed by Dr Trisha Macnair in July 2008