BBC News Online's health team examines the condition, which affects one in every 100 pregnancies.

What is it?

Eggs make their way from the ovaries to the womb through the fallopian tubes, where they may be fertilised by a sperm.

The fertilised egg continues on to the womb, where it implants itself to the wall and continues to grow.

However, sometimes the embryo implants itself outside the womb, most often in the fallopian tubes themselves, and this is known as an ectopic pregnancy.

The embryo can also implant in the ovary, the abdomen, and in the cervix.

What causes it?

Anything that obstructs or slows the movement of eggs can increase the risk.

Infections in the fallopian tubes, such as chlamydia, can leave them scarred, which will hinder movement, or there may be a physical blockage caused by previous surgery or injury.

Hormones - particularly those used in contraceptive pills and devices - can also affect the rate of movement of the egg.

Who gets it?

As well as women in the categories above, those who are taking the progesterone-only Pill - or mini Pill - but become pregnant regardless are three times more likely to suffer an ectopic pregnancy.

In cases where the morning after contraceptive pill is used to no avail the risk of the pregnancy being ectopic rises 10-fold.

Women who become pregnant despite having been surgically sterilised have a 60% chance of an ectopic pregnancy.

Women receiving fertility treatment are also at greater risk, as are women who have had previous ectopic pregnancy.

Ectopic pregnancies are on the rise with the rate nearly tripling from 1970 to 1980.

What are the risks?

With an ectopic pregnancy, the embryo can rupture the fallopian tube, leading to massive internal bleeding - and possibly death - for the mother, and loss of the baby.

If the woman survives this, her fertility is likely to be greatly reduced and her chances of going through the same experience are increased.

What is the treatment?

Because of the life threatening nature of the condition, early diagnosis is essential and doctors recommend terminating the pregnancy.

If the pregnancy is allowed to continue and the tube ruptures, doctors have to remove it, reducing the woman's fertility.