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 cavity of 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 at the end of the Fallopian tube. The ovum then makes its way along the Fallopian tube towards the womb. During the course of this journey it may encounter a man’s sperm, in which case it may be fertilised.

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 or delayed while progressing along 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. This can sometimes cause internal bleeding, causing pain requiring immediate medical attention.

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

Ectopic pregnancy diagram
  • 80% are Ampullary (in the middle part of the fallopian tube)
  • 15% are Isthmic (in the upper part of the fallopian tube close to the uterus)
  • 5% are Fimbrial (at the end of the tube)
  • 2% are Interstitial (inside the part of the fallopian tube that crosses into the uterus)
  • <1% are within a Caesarean Section scar on the uterus
  • <1% are Cervical (on the Cervix)
  • <1% are Cornual (within an abnormally shaped uterus)
  • <1 % are Ovarian (in or on the ovary)
  • <1% are Intramural (in the muscle of the womb)
  • <1% are Abdominal (in the abdomen)
  • <1% are Heterotopic pregnancies

Find out more about the specific types of ectopic pregnancy

Click on each one to read more.

 Ampullary, Isthmic and Fimbrial Pregnancy

Tubal ectopic pregnancy (ampullary, isthmic and fimbrial)

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 tube 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 fertilised egg to the cavity of the uterus which takes about four days. 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 be slow for no obvious reason. 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 potentially dangerous ectopic pregnancy.

Interstitial/Cornual Pregnancy

Interstitial Pregnancy

An 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 or may be difficult to see on a scan very early on. 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 may recommend 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.

In the scar of a caesarean section

Caesarean scar pregnancy

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. Caesarean scar ectopic pregnancies are when the fertilised egg implants into the gap in the muscle of the uterus from a previous Caesarean section. The pregnancy may then grow out of the uterus or onto the cervix and cause torrential internal or vaginal bleeding. In some pregnancies the placenta develops so that only part of it is within the scar and these pregnancies may proceed to delivery of a live baby, but with risk of significant bleeding from the mother and hysterectomy at the time of delivery. Early treatment options include removing the pregnancy using suction and a cervical stitch or keyhole surgery, or using Methotrexate injection/s. 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 hospitals 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.

Cervical Pregnancy

Cervical Pregnancy

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 vaginal haemorrhage. The cervix is highly vascular (lots of blood vessels) and, when the pregnancy separates from the cervix blood transfusions are usually essential. An emergency hysterectomy has historically been the only option as the diagnosis was not often made before rupture; however, planned conservative management of a cervical ectopic pregnancy using suction evacuation and a cervical stitch or Methotrexate are now potential treatments to preserve the woman’s fertility if the diagnosis is made before it becomes an emergency. 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.

Cornual / Rudimentary Horn Pregnancy

This is another rare type of ectopic pregnancy that only occurs in a uterus that has not formed fully. A normally shaped uterus develops from tow halves that join together. Sometimes these two halves do not meet and this leaves one banana shaped (unicornuate) side which is not in contact with the cervix and vagina and another nubbin of uterus on the opposite side (that is not usually in contact with the cervix and vagina, called a rudimentary horn). Both sides have their own fallopian tube. Sperm can reach deep inside via the one sided uterus that is in contact with the vagina, but the opposite tube may pick up the fertilised egg and transport it into the rudimentary horn. Because the rudimentary horn often has a thick muscular wall, these pregnancies may advance into the second or even third trimester before they cause catastrophic rupture. The thick wall also makes them more difficult to diagnose, as rudimentary horn may be assumed to be a normal uterus. Treatment is to terminate the pregnancy by surgically removing the rudimentary horn and its fallopian tube. If the pregnancy is advanced, this is sometimes difficult to do without also removing the ovary on the same side.

Ovarian Pregnancy

Ovarian Pregnancy

These are difficult to diagnose as they look very similar to a tubal ectopic pregnancy that is stuck to the ovary or a ‘corpus luteum’ which is the place that the egg was released from, so they are often not diagnosed until surgery. 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 due to bleeding. 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.

Intramural Pregnancy

Intramural Pregnancy

This is a term that means ‘in the wall’ and refers to a pregnancy that implants outside the cavity of the womb, but within it’s muscular wall. These pregnancies are thought to occur when the uterus has been scarred by previous surgery or a condition called adenomyosis. Again, they can be difficult to diagnose as it can be hard to see the cavity as separate to the pregnancy. The pregnancies are also inaccessible, which makes them difficult to treat by removing the pregnancy. Methotrexate may be advised.

Abdominal Pregnancy

Abdominal Pregnancy

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.

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, it is possible to have a twin pregnancy and 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.

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.