One night, I received an urgent call from the hospital informing me that a patient - Mrs T - was in shock.

Two months pregnant, Mrs T, a 30-year-old dance teacher, had collapsed while out for dinner.

'There was sudden pain in my stomach and I felt sick. I almost fainted," she recalled. "Fortunately, my hubby was with me and he rushed me to the hospital."

I rushed to the A&E department to find an extremely pale Mrs T in pain on the examination couch. Her blood pressure was low, her pulse weak and rapid, and her abdomen was slightly bloated and tender to the touch.

Further examination showed slight bleeding from the vagina. The womb was tender and no foetus was detected on ultrasound examination. Instead, the womb was surrounded by a large amount of fluid.

Mrs T was quickly resuscitated and rushed to the operating theatre for an emergency operation. When the abdomen was opened, 11/2 litres of blood gushed out. The right fallopian tube had burst and there was active bleeding from the rupture site. The fallopian tube was quickly removed to stop the bleeding.

Mrs T had an ectopic pregnancy - and the emergency operation saved her life.

Ectopic pregnancy happens in one out of about 300 pregnancies. It is a serious, life-threatening condition where the foetus is implanted outside the womb, usually in the fallopian tube (tubal pregnancy), as in Mrs T's case.

Very rarely, it can occur in the ovary, the abdomen, or the neck of the womb.

In a normal pregnancy, fertilisation of the egg occurs at the far end of the fallopian tube. The foetus then starts to grow. Within three to seven days, it travels down the tube to the womb and attaches itself there.

If the tube is partially obstructed (usually a result of scarring from previous inflammation), this will slow the passage of the foetus which will then embed itself in the tube instead of going all the way to the womb.

Unlike the womb, the tube has a thin muscular wall. It will eventually burst from the growing foetus, resulting in severe internal bleeding.

Inflammation of the fallopian tube can be caused by an Intrauterine Contraceptive Device (IUCD) or previous pelvic surgery.

Recent research also links ectopic pregnancy to an insidious sexually transmitted infection called chlamydia. This germ affects the cervix, womb, fallopian tubes and pelvis - yet with few symptoms. The sufferers are usually unaware of it.

In Mrs T's case, the only relevant history that could have contributed to ectopic pregnancy was that she had an abortion a few years ago and had an IUCD inserted at the same time.

'The IUCD was removed six months prior to this pregnancy as my husband and I decided to start a family, and I was also bothered by the yellow, foul-smelling vaginal discharge,' she said.

Not all ectopic pregnancies are as dramatic as Mrs T's.

The symptoms may be minimal and can even be confused with those of a threatened miscarriage or gastric discomfort.

Mrs P, 33, had a particularly bad run of medical misfortune. After having a miscarriage with her first child, she quickly became pregnant again. A few weeks into this second pregnancy, however, she started to bleed and feared she might lose her baby again.

A scan when she was six weeks pregnant made me suspicious of an ectopic pregnancy as there was no pregnancy sac in the womb. She also had very slight abdominal pain, which she regarded as muscle stitch.

During laparoscopy - where a long telescope connected to a video camera was inserted into her abdomen - her left tube was found to be distended with a foetus. The tube was on the verge of bursting. The foetus was removed and the tube preserved.

This case illustrates the importance of an early antenatal check-up.

The psychological impact of ectopic pregnancy and the uncertainty about the woman's future fertility can be long-lasting. It is like any other pregnancy loss. The patient has to face a bereavement and, often, her own mortality. There may be post-traumatic stress with panic attacks and high levels of anxiety.

The husband, too, may be badly affected.

'Months after the incident, I would often hear sobbing sounds from the toilet. I knew my hubby was crying. Sometimes, he hid himself in the toilet for hours,' Mrs T recalled.

It took the couple another year before they picked up enough courage to try for a baby again. About 85 per cent of women who have had an ectopic pregnancy are able to have a normal pregnancy again. Mrs T is now a proud mother of two healthy children.

Dr Peter Chew is a senior consultant gynaecologist and obstetrician at Gleneagles Medical Centre. He is the founder chairman of aLife, a charitable organisation with a mission to nurture and promote healthy family life.

This article was first published in Mind Your Body, The Straits Times on Apr 16, 2008.