What is an ectopic pregnancy?

Ectopic pregnancy is a common, life-threatening condition that affects 1 in 80 pregnancies. Put very simply, it means “an out-of-place pregnancy”. It occurs when a woman’s ovum (egg), that has been fertilised, implants (gets stuck somewhere) instead of moving successfully down her fallopian tube into the womb to develop there. The most common place for an ectopic pregnancy is the fallopian tube but there are many other sites where an ectopic pregnancy can be located. It is, sadly, not possible to move an ectopic pregnancy.

Each month, before a woman has her period, one of her ovaries produces an ovum that is drawn into one of the fine finger-like tubes called fimbriae, passes through it, and is deposited into the end of the fallopian tube. The ovum then makes its way towards the womb. During the course of this journey it may encounter a man’s sperm, in which case it becomes fertile.

If it is fertilised, the ovum implants itself into the special lining of the womb (renewed each month) called the endometrium and becomes a baby. If it is not fertilised, then both ovum and lining are discharged in the menstrual flow (period), a fresh lining is prepared and a new ovum begins to ripen within the ovary.

In the case of an ectopic pregnancy, the fimbriae can fail to catch the ovum so the ovum becomes fertilised outside the reproductive system or, more commonly, the fertilised ovum becomes caught while progressing down the fallopian tube. In this case, the baby continues to grow inside the tube where it can cause the tube to burst or otherwise severely damage it. In either case, a serious medical condition is likely to develop, requiring immediate attention.

The diagram shows where ectopic pregnancies are most likely to occur:

Ectopic pregnancy diagram
  • 80% are Ampullary (in the upper part of the fallopian tube)
  • 12% are Isthmic (in the lower part of the fallopian tube)
  • 5% are Fimbrial (caught in the fimbriae)
  • 2% are Interstitial/Cornual (inside the uterus but outside the cavity)
  • 1.4% are Abdominal (in the abdomen)
  • 0.2% are Ovarian (in or on the ovary)
  • 0.2% are Cervical (on the Cervix)

Find out more about the specific types of ectopic pregnancy

Click on each one to read more …

Ampullary, Isthmic and Fimbrial Pregnancy (97%)

Ampullary, Isthmic and Fimbrial Pregnancy (97%)

The fallopian tubes (or oviducts) are small, hollow muscular tubes, each about ten centimetres long. The outer half lies next to, but not attached to, its ovary. The tubes have a delicate mucous membrane lining inside the tube, thrown up into folds, which almost fill each tube (see diagram below). The diameter and the number of folds increase as the tube nears the ovary and forms the fimbriae – tiny finger-like projections that move and create a suction effect to draw the ovum to the tube.In the lining of the tubes, half the cells are mucus-secreting and half have cilia – tiny hair like projections which waft gently to propel these secretions towards the uterus. The muscular wall of each tube becomes thicker towards the uterus, and has a natural peristaltic action (contraction and relaxation to create a pumping effect) which assists the movement of mucus. An egg, released at ovulation, is picked up by the fallopian tube fimbriae, and the tube is responsible for the transport of the egg to the uterus which takes about four days.After sexual intercourse with a man, sperms swim up the fallopian tubes, some arriving within fifteen minutes of their being deposited in the vagina, after passing through the cervix and uterus. Fertilisation usually occurs in the outer part of the tube near to the ovary and the first cell division into two new cells takes place within twelve to twenty hours, and successive divisions (doubling the number of cells each time) happen every fifteen hours. A bundle of sixty four cells reaches the uterus to implant six to seven days after ovulation, by which time the natural female hormones have prepared the uterine lining cells (endometrium). The embryo burrows into the endometrium and starts to form a placenta.

It is not difficult to imagine how the delicately folded tube linings with specialised cells can become damaged by inflammation or infection, and/or the transportation of a developing embryo to the uterus may fail. In the meantime, the embryo is still trying to develop and has a natural invasive nature, so it can implant in the tube or fimbriae to form a placenta, resulting in a dangerous ectopic pregnancy.

Interstitial/Cornual Pregnancy (2%)

Interstitial/Cornual Pregnancy (2%)

A cornual pregnancy or interstitial pregnancy is a rare type of ectopic pregnancy that occurs when the fertilised egg implants in that part of the fallopian tube buried deep in the wall of the uterus. Pregnancies of this kind are difficult to diagnose as they appear to be in the uterus on a scan. They are particularly dangerous as they can progress further and tend to rupture later, having the potential to damage both the wall of the uterus and the fallopian tube. If diagnosed early enough, doctors will often select medical treatment with methotrexate if the patient is a suitable candidate for this, as surgery for an interstitial pregnancy can involve surgery to the actual uterine wall and this could result in the uterus being weakened.It is possible to have successful uterine pregnancies after an interstitial pregnancy. Your doctor will assess you carefully and consider the need for an elective caesarean section to deliver any subsequent pregnancy and the preferred method of delivery will depend on the extent of the surgery necessary on the uterine wall to resolve the ectopic pregnancy.

Abdominal Pregnancy (1.4%)

Abdominal pregnancies, in most instances, are thought to have begun in the fallopian tube and then separated from the wall of the fallopian tube, floating into the abdominal cavity to then reattach to one of the structures in the abdomen. The pregnancy can progress and may go undetected until many weeks in to the pregnancy. There are some accounts of abdominal pregnancies surviving to be delivered with an abdominal operation but these are incredibly rare.
Ovarian Pregnancy (0.2%)

Ovarian Pregnancy (0.2%)

The ovary is a highly vascular structure. An ectopic pregnancy located on or in the ovary will usually require surgery involving either the partial or complete removal of the ovary. If the ovary is only partially removed, it may recover and continue to produce eggs as before. However, even if it does not produce eggs any longer or is removed completely, the other ovary is perfectly capable of producing an egg every cycle, enabling the woman to conceive naturally in the future.

Cervical Pregnancy (0.2%)

Cervical Pregnancy (0.2%)

Cervical pregnancies are one of the rarest forms of ectopic pregnancy and are thought to be of special concern because of the risk of life-threatening haemorrhage. The cervix is highly vascular (lots of blood vessels) and, should the pregnancy cause a rupture, blood transfusions are usually essential. An emergency hysterectomy has historically been the only option; however, conservative management of a stable, cervical ectopic pregnancy using methotrexate or potassium chloride is now the treatment of choice to preserve the woman’s fertility.Prior surgical trauma, including dilatation and curettage of the cervix (D&C), has been identified as one of the leading risk factors for a cervical ectopic pregnancy.

Heterotopic Pregnancy

Heterotopic Pregnancy

Heterotopic pregnancy is the term used to describe a condition where there is the co-existence of an intrauterine pregnancy with an ectopic pregnancy. Although it is rare (occurring in fewer than 2% of ectopic pregnancies) it is possible for one embryo to implant in the uterus and another elsewhere. It is possible for the co-existing intrauterine twin to survive in approximately 30% of diagnosed cases of heterotopic pregnancy, despite the woman being treated surgically for the condition.

In the scar of a caesarean section

In the scar of a caesarean section

Research indicates that this kind of ectopic pregnancy appears to be increasing, most likely due to the impact of elective caesarean section delivery which was much less common 10 years ago than today. It is where the egg implants in the C-section scar where the uterus is not strong enough to sustain the pregnancy without rupturing. A ruptured uterus is life-threatening.Treatment, to some extent, is determined by the gestational age of the pregnancy (how many weeks pregnant you are). If the pregnancy is very early then the pregnancy tissue is usually removed using a thin suction catheter passed through the cervix, with no other treatment being necessary. Slightly later a stitch may be put in the cervix as well to stop any bleeding from the caesarean scar once the procedure has been carried out. After 10 weeks management may involve a number of approaches including both surgery and the use of methotrexate.The treatment of caesarean scar pregnancies is potentially difficult so management has to be individualised on a case by case basis. Despite appearing to increase in incidence, they are still relatively uncommon and so some hospital see very few of them. Accordingly, there are moves to focus care in these cases to regional units with experience of these problems both to optimise care and to collate information to make sure there is a better evidence base to inform treatment decisions in the future.

One of our medical advisors, Jackie Ross, Consultant Gynaecologist at Kings College Hospital helps to explain ectopic pregnancy in this video

If you would like more information on menstruation (having your period) generally and how pregnancy is achieved, we recommend watching this short video from NHS Choices NHS Choices – Menstrual Cycle animation.

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