Tubal Pregnancy

What is a Tubal Pregnancy?

Tubal pregnancy is a type of ectopic pregnancy* which occurs when a fertilised egg implants within the mother's fallopian tubes. It is the most common site of implantation for ectopic pregnancies (accounting for 93-97%⁶), although fertilised ova may also implant in the ovaries and peritoneal cavity, as shown in diagram 1^1,3.

* Ectopic pregnancy refers to pregnancies with blastocyst implantation in anatomical sites other than the uterus. Ectopic implantation of the blastocyst occurs in roughly 1% of pregnancies, and is a leading cause of maternal mortality during the 1st trimester.^1,5,8

Area of Implantation

Within the fallopian tubes themselves, several different sites of implantation occur with varying frequency. Most commonly, the blastocyst implants within the ampulla or isthmus of the fallopian tubes, though implantation in the fimbria of the fallopian tube may also occur⁷.

Blastocyst implantation due to fallopian tube obstruction.

Risk Factors for Tubal Pregnancy

Any factor which slows the passage of the fertilised egg through the fallopian tubes increases the risk of tubal pregnancy. This may include scarring or chronic inflammation (chronic salpingitis) of the fallopian tubes, however, roughly 50% of cases have no anatomical explanation for the pathological implantation¹. Other risk factors increasing the risk of ectopic pregnancy include^{2, 4, 5, 6}:

Smoking
Pelvic Inflammatory Disease
Endometriosis
Prior ectopic pregnancy
Past surgery involving the fallopian tubes
Tubal abnormalities or congenital defects within the fallopian tubes
Age > 35
Presence of an intra-uterine device during fertilization
Some assistive reproductive technologies i.e. In Vitro Fertilization or Gamete Intra-Fallopian Tube Transfer (GIFT)

Diagnosis and Intervention

Despite its improper placement, tubal pregnancies normally progress in a similar fashion to other pregnancies, including hormone release causing cessation of menstruation and physiological changes to the female body¹. In around half of the occurrences, changes to the endometrium of the uterus will still take place, causing decidualization and hypersecretion of the endometrium.
Embryonic progression similarly occurs for the implanted blastocyst, with the developing placenta burrowing into the lining of the fallopian tubes in a similar fashion to within the uterus. In some cases of tubal pregnancy, the inadequate blood supply may prevent further embryonic growth and lead to spontaneous resolution of the ectopic pregnancy⁶.
However, progression of placental growth, amniotic sac formation and decidual formation causes the distension of the affected fallopian tube, and trophoblastic invasion into the lining of the fallopian tubes may eventually cause rupture, resulting in haematosalpinx and/or intraperitoneal haemorrhage^1,6. Tubal pregnancy rupture may be indicated by intense abdominal pain (with sudden onset)and is often followed by shock¹.

Signs and Symptoms of Rupture

Signs of ectopic pregnancy rupture with intraperitoneal haemorrhage include hypovolemia (decreased blood volume), tachycardia, diaphoresis (profuse perspiration) and shock⁶. Tubal ruptures are potentially fatal for the woman and require immediate surgical intervention.

Diagnostic Techniques

Prior to rupture, tubal pregnancies may be diagnosed through imaging the abdomen - most commonly using transvaginal ultrasound. Combination of imaging with pregnancy hormone level estimations (via a blood test) are currently used to provide a diagnosis, and may detect tubal implantation early within the pregnancy⁶. A physical examination of the pelvis to determine the size of the uterus and the presence of growths within the area may also be helpful initially².
During the first 8 weeks of a normal pregnancy, b-hCG levels are expected to double every 48 hours, an increase which is not mirrored in the majority of tubal pregnancies, where b-hCG levels remain low or rise at a slower rate⁷. This is due to the inability of the fallopian tubes to support indefinite trophoblastic growth - limitations in blood supply to the fallopian tubes retard trophoblastic growth and the corresponding decreased hormone signalling from the trophoblast may also result in corpus luteum dysfunction (low serum progesterone levels)⁶. Vaginal bleeding may similarly result from inadequate hormone levels, as the decidualized endometrium begins to slough away⁶.

Symptoms of Tubal Pregnancy

Vaginal bleeding and pelvic or abdominal pain are the main symptoms of a tubal pregnancy²; any woman with possible pregnancy who develops these symptoms should seek further medical investigation.

Resolution of the Tubal Pregnancy

Ectopic pregnancies are not able to continue to term, and are unable to progress to the point where the child is capable of extra-uterine survival. Thus, abortion of the pregnancy is necessary to save the woman's life in cases where spontaneous resolution of the pregnancy by tubal abortion or reabsorption does not occur. As the natural process may take up to 50 days, 'expectant management' (where the woman is monitored with repeated hCG measurements and transvaginal ultrasounds in expectation of spontaneous resolution) should only be used where the woman is medically stable, has access to immediate medical assistance and is willing to receive follow-up testing⁷. Otherwise, medical abortion through administration of methotrexate or surgical abortion through excision of the products of conception may be used.
Due to the non-viable state of the pregnancy and the potentially fatal effects to the woman, pursuit of abortion is an ethical and necessary decision⁵.

References

Kumar, V., Abbas, A.K., & Aster, J.C. (Eds.). (2013). Robbins Basic Pathology (9th Ed.). p. 701. Philadelphia: Saunders.
Ectopic Pregnancy - Topic Overview (2013). Retrieved July 26, 2014 from http://www.webmd.com/baby/tc/ectopic-pregnancy-topic-overview
What is an Ectopic Pregnancy? (n.d.). Retrieved July 26, 2014 from http://www.ectopic.org.uk/patients/what-is-an-ectopic-pregnancy/
Storck, S. (February 2014). Ectopic pregnancy in MedlinePlus. Maryland: A.D.A.M., Inc. Retrieved from http://www.nlm.nih.gov/medlineplus/ency/article/000895.htm
Best, M. (2012). Fearfully and Wonderfully Made. Kingsford, Australia: Matthias Media.
Crochet, J.R., Bastian, L.A. & Chireau, M.V. (2013). Does this woman have an ectopic pregnancy? The rational clinical examination systematic review. Journal of American Medical Association, 309(16), pp. 1722-1729.
McQueen, A. (2011). Ectopic pregnancy: risk factors, diagnostic procedures and treatment. Nursing Standard, 25(37), pp. 49-56.
Tenore, J.L. (2000). Ectopic Pregnancy. American Family Physician, 61(4), pp.1080-1088.

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