Ovarian ectopic pregnancy (OEP) is a rare type of ectopic pregnancy in which the fertilized ovum implants into the ovary.

Abstract: Ovarian ectopic pregnancy (OEP) is a rare type of ectopic pregnancy in which the fertilized ovum implants into the ovary. There appears to be a strong association of OEP with intrauterine devices (IUD). Ultrasound is the primary diagnostic tool for this condition however timely and exact diagnosis is challenge because the ultrasonographic appearances  overlap with the appearance of a physiological corpus luteum or hemorrhagic ovarian cyst. The final diagnosis is based on intraoperative findings and histopathological observations. Surgical intervention is recommended as the first-line option,having both diagnostic and therapeutic value.

Authors: Dr Linh K Phan1, Dr Nguyen T Ha1

1. Imaging Diagnositic Department, Tudu Maternal Hospital Vietnam

Reviewers: Karen Fung-Kee-Fung

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An ectopic pregnancy is characterized by implantation and development of an embryo outside of the uterine cavity. Ovarian ectopic pregnancy occurs when a fertilized ovum implants into the ovary [1]. 


OEP is a rare event, with estimated frequency ranging from 1 in 7000 to 1 in 40.000 live births [1]. It accounts for 3% of all ectopic pregnancies, similar to the incidence of interstitial ones [2].

Classification and Pathogenesis

OEP is classified as primary or secondary ovarian ectopic pregnancy. The cause of primary OEP remains obscure. It is hypothesised that due to ovulatory dysfunction, the ovum is fertilized while still within the follicle, before the follicle being expelled from the ovary [1]. Most OEP seem to be secondary due to the reflux of a fertilized ovum from the fallopian tube to the ovary [3]. The cases of OEP after assisted reproductive technologies reported in the literature support the theory of reflux. 
Ovarian ectopic pregnancy can also be further categorized into intra-follicular and extra-follicular. Intra-follicular OP, due to failure of follicular expulsion, occurs when the ovum is fertilized within the follicle inside of the ovary and is very rare. Extra-follicular OEP occurs when the ovum is fertilized in the fallopian tube or intra-abdominal cavity and subsequently migrates to and implants on the surface of ovary [4]. However, classification of OEP into primary or secondary does not affect the clinical management.

Risk factors

The actual cause of OEP is unknown, as the usual causative factors of ectopic pregnancy seem not to be involved. Some theories suggest that the abnormal implantation that occurs in OEP is a result of the following: (1) Embryo migration related to the presence of certain conditions that damage fallopian tube epithelium, (2) An obstacle to the release of the ovum from the ruptured follicle, (3) Inflammatory thickening of the tunica albuginea [5,6]

There seems to be an especially strong association of ovarian pregnancies with intrauterine devices (IUD). An IUD is found in 14% to 30% of patients with a non-ovarian extrauterine pregnancy, while it is found in 57% to 90% of patients with a primary ovarian pregnancy [3,5]. The theory behind this is that although the IUD provides protection from intrauterine implantation, it does not prevent ovarian implantation. Specifically, it is thought that the IUCD may potentiate ovarian implantation due to changes in prostaglandin synthesis that subsequently increases tubal peristalsis [4].

Conception through the use of assisted reproductive techniques is also related to the increased OEP’s incidence similar to  ectopic pregnancies in other locations [3,5].

Recurrence risk

Recurrence risk of ovarian ectopic pregnancy is rare.


Clinical symptoms and signs of ovarian pregnancy are variable and similar to a tubal ectopic pregnancy, including: amenorrhea, irregular vaginal bleeding, lower abdominal pain, normal uterine size, adnexal tenderness, palpable adnexal mass, … and sometimes may be totally asymptomatic. Abdominal examination may show abdominal tenderness with/without guarding sign of peritoneum irritation. In the ruptured ovarian pregnancies, acute pain and hypovolemic shock may happen due to haemorrhage. 

A single measurement of the quantitative β hCG level alone cannot differentiate an intrauterine pregnancy from an ectopic pregnancy.  Therefore, serial quantitative β hCG levels correlated with serial transvaginal ultrasound findings are recommended to determine an early intrauterine pregnancy from ectopic pregnancy. An abnormal increasing of serial beta β hCG allows to recognize of an abnormal implantation but it’s not specific to OEP.

In 1878, Spiegelberg proposed the criteria for diagnosing ovarian pregnancy: (1) ipsilateral tube must be intact (2) gestational sac must occupy a position in ovary (3) ovary must be attached to the uterus through the utero-ovarian ligament, (4) there must be ovarian tissue attached to the pregnancy in the specimen [7]. These criteria are continued to be the standard for the diagnosis of ovarian pregnancy at the time of surgery. They are useful to differentiate ovarian pregnancy from other types of ectopic pregnancy but can not applied in ultrasound.  

Transvaginal ultrasound plays an important role in establishing the preoperative diagnosis. Some criteria are very suggestive for sonographic localization of ovarian pregnancy: (1) An empty endometrial cavity; (2) A gestational sac with a yolk sac/fetal pole (+/-) cardiac motion, that is inseparable from adjacent ovarian parenchyma; (3) A wide echogenic ring with an internal echolucent area on the ovarian surface, (4) The presence of ovarian cortex, including corpus luteum or follicles around the mass; the echogenicity of the ring usually greater than that of the ovary tissue [4]. 

The key diagnostic feature is the inability to separate the pregnancy from the ovary on gentle palpation with the ultrasound probe during the examination. However, this finding is not entirely specific as it may also be present in tubal pregnancies which are firmly adhered to the uterus or ovary [5].  The presence of a yolk sac or embryo within the ovarian cortex is highly specific of an ovarian pregnancy. 

Differential diagnosis

In an absence of yolk sac or fetal pole on ultrasound imaging, an ovarian pregnancy can be misinterpreted as  a hemorrhagic ovarian cyst or corpus luteum. A corpus luteum may have a ring-like appearance, but in the majority of cases, a corpus luteum is less echogenic than the ovary itself [6]. Attempting to use Color Doppler ultrasonography to distinguish a gestational sac from a corpus luteum is useless, because both have the “ring-of-fire” sign. Follow-up ultrasound findings should demonstrate  a corpus luteum cyst demonstrating progressive involution with increasing crenulation of its margins, whereas an ovarian pregnancy will grow, with marked thickening of the circumferential echogenic margins and appearance of a yolk sac and fetal pole within the gestational sac [8]. Sometimes, only the presence of trophoblastic tissue during the histologic examination of material of a bleeding ovarian cyst definitively proves that an ovarian pregnancy was the cause of the bleeding [9].

A distal tubal ectopic pregnancy that is close to the ovary can also be misdiagnosed as an OEP. Free movement between the ovary and an adnexal mass on palpation during ultrasound (sliding sign) can assist in differentiating intraovarian mass (ovarian pregnancy) from extraovarian mass (tubal pregnancy) [7]. Tubal ectopic pregnancies also have ring-like appearance but the ring has much thinner wall compared with ovarian pregnancy.

Implications for sonographic diagnosis

The incidence of ectopic pregnancy has been steadily increasing, likely related to the increase in rate of assisted reproductive technologies and the improved transvaginal ultrasound technology. It is still the leading cause of haemorrhage-related maternal mortality in the first trimester due to the overlapping clinical symptoms and ultrasound findings with other early pregnant complications. Therefore, an early diagnosis is the key point for a good outcome. 


Ideally, treatment should be commenced before rupture of the OEP. The proposed methods for management are similar to other ectopic pregnancies and the decision should be made based on the clinical manifestations, the desire for future pregnancy, and available treatment protocols at the medical facility.

Surgical intervention has both a diagnostic and a therapeutic value and is recommended as the first-line option. The surgical approach consists of laparoscopy/ laparotomy with the final goals of removal of ectopic pregnancy tissue, achieving hemostasis, and preservation of healthy ovarian tissue. In ruptured OEP, urgent surgery should be taken immediately to prevent maternal complications. Laparotomy is urgently required  for hemodynamic instability such as hypovolemic shock or  significant hemoperitoneum. In unruptured OEP, laparoscopy is  advantageous due to its non-invasive nature, with less intraoperative blood loss and shorter hospital admission. A prospective study including 12 cases of ovarian pregnancies were managed by laparoscopy, resulting in no cases requiring conversion to laparotomy or required further treatment [10]. Depending on the size of mass, degree of haemorrhage and the desire for future childbearing, the operator can consider cystectomy or wedge resection. 

Medical management remains controversial. Relevant literature is limited on this subject. Its advantage is to preserve ovarian tissue, and therefore can be considered in young women desiring subsequent pregnancy. Criteria have been suggested for the use of methotrexate if the following criteria are met: (1) no signs of hemodynamic compromise; (2) no evidence of blood in the pelvis; (3) pregnancy size must be < 3.5 cm with no fetal heart activity; and (4) b-hCG level should be < 3,500 IU/L [11].


OEP, like any other type of ectopic pregnancy, is associated with a considerable risk of maternal morbidity and mortality and risk of rupture of OEP is a life-threatening complication. Ovarian pregnancies usually terminate in rupture during the first trimester in 91% of the cases, in 5.3% cases in the second trimester and in 3.7% cases in the third trimester [12]. Early diagnosis plays a vital role in management and reducing maternal complications. 


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This article should be cited as: Linh K Phan, Nguyen T Ha, Ovarian Ectopic Pregnancy, Visual Encyclopedia of Ultrasound in Obstetrics and Gynecology, www.isuog.org, January 2022.

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