Aetiology
Two broad categories of conditions lead to ectopic pregnancy: 1) conditions that hamper the transport of a fertilised oocyte to the uterine cavity, and 2) conditions that predispose the embryo to premature implantation. However, more than half of diagnosed ectopic pregnancies are not associated with any known risk factors.[16] Pelvic infection can increase risk by distorting fallopian tube anatomy. Factors associated with increased risk of ectopic pregnancy include smoking, multiple sexual partners, concomitant use of IUD, prior fallopian tube surgery, in utero diethylstilbestrol exposure, previous genital infections or pelvic inflammatory disease, infertility and in vitro fertilisation, age <18 at first sexual intercourse, black race, and age >35 years at presentation.[17][18][19]
Pathophysiology
Effective transport of embryos in the fallopian tube requires a delicately regulated complex interaction between the tubal epithelium, tubal fluid, and tubal contents. This interaction ultimately generates a mechanical force, composed of tubal peristalsis, ciliary motion, and tubal fluid flow, to drive the embryo towards the uterine cavity. This process is subject to dysfunction at many different points that can ultimately manifest as ectopic pregnancy.[20]
Oocyte migration difficulty is most often associated with abnormal fallopian tube anatomy. This can result from tubal pathology (e.g., chronic salpingitis, salpingitis isthmica nodosa), tubal surgery (e.g., reconstruction, sterilisation), or in utero diethylstilbestrol exposure. It is thought that alterations in molecular signalling between the oocyte and the implantation site may make an ectopic pregnancy more likely.[17][21] A number of molecular factors are under investigation for possible involvement in premature implantation. These factors include cellular and extracellular matrix proteins such as lectin, integrin, matrix-degrading cumulus, prostaglandins, growth factors, and cytokines.[22]
Studies have not supported a role for chromosomal abnormalities in abnormal implantation. Karyotypes of the chorionic villi from 30 viable surgically removed ectopic pregnancies did not find any difference compared with the control intrauterine pregnancies.[23][24]
As the ectopic grows, the outer layer of the fallopian tube stretches. This ultimately leads to tubal rupture and bleeding.[Figure caption and citation for the preceding image starts]: Blood in abdomenFrom the collection of Dr Sina Haeri; used with permission [Citation ends].
Classification
Tubal pregnancy (97%)
May implant in ampulla (73.3%), isthmus (12.5%), fimbria (11.6%), and interstitium and cornua (2.6%).[1]
Ovarian pregnancy (1% to 3%)
Strict histopathological diagnostic criteria apply.[3]
Cervical pregnancy (<1%)
Often presents with profuse and painless bleeding.[4][5]
Interstitial pregnancy (2%)
Trophoblast implants at junction of proximal fallopian tube and muscular wall of the uterus.[6]
Hysterotomy scar pregnancy (<1%)
Implantation into the myometrial defect at the site of a previous uterine incision.
Abdominal pregnancy (1.4%)
May be primary from direct implantation of the blastocyst or secondary from expulsion of the embryo from the fallopian tube.[7]
Heterotopic pregnancy (1:4000)
Two concurrent pregnancies, one intrauterine and the other ectopic. Incidence is rising, approaching 1% among women undergoing IVF.[8] In spontaneous conception, the incidence remains low (1:30000).
Ectopic pregnancy after hysterectomy
There have been numerous case reports of ectopic pregnancies following both total and supracervical hysterectomies. Although this condition is extremely rare, clinicians should be aware of the possibility of its occurrence. Provided that at least one ovary has been retained, a pregnancy test should be performed for a woman of reproductive age who has previously had a hysterectomy and presents with abdominal pain of unknown origin.[9]
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