In very rare occasions the pregnancy may find a sufficient foothold outside the ovary to continue as an abdominal pregnancy, and an occasional delivery has been reported.y

Diagnosis
The diagnosis is made in asymptomatic pregnant women by obstetric ultrasonography. On pelvic examination a unilateral adnexal mass may be found. Typical symptoms are abdominal pain and, to a lesser degree, vaginal bleeding during pregnancy. Patients may present with hypovolemia or be in circulatory shock because of internal bleeding.Ideally, ultrasound will show the location of the gestational sac in the ovary, while the uterine cavity is "empty", and if there is internal bleeding, it can be identified. Because of the proximity of the tube, the sonographic distinction between a tubal and an ovarian pregnancy may be difficult. Serial hCG levels generally show not the normal progressive rise. In a series of 12 patients the mean gestation age was 45 days.Histologically, the diagnosis has been made by Spiegelberg criteria on the surgical specimen of the removed ovary and tube. However, the tube and ovary are not usually removed as sonography allows for earlier diagnosis and surgeons strive to preserve the ovary. Prior to the introduction of Spiegelbergs criteria in 1878, the existence of ovarian pregnancy was in doubt; his criteria helped to identify the ovarian pregnancy from other ectopics:
The gestational sac is located in the region of the ovary. The gestational sac is attached to the uterus by the ovarian ligament. Ovarian tissue is histologically proven in the wall of the gestational sac.
The incidence has been reported to be about 1:3,000 to 1:7,000 deliveries. History
In 1614 Mercier (also shown as Mercerus) described ovarian pregnancy for the first time, as a condition separate from a tubal pregnancy. Once the study of physiology emerged, Boehmer classified extra-uterine pregnancy into three classes: abdominal, ovarian, and tubal. There were many doubters that such a condition existed, particularly Mayer, who wrote an essay not only denying the existence of ovarian pregnancy, but demonstrating that recorded cases to that time were other conditions. Then Cohnstein proposed four criteria that would need to be present for ovarian pregnancy exist. His requirements were: 1) absence of the ovary on the side in which the alleged pregnancy was located; 2) connection of the uterus and sac via an ovarian ligament; 3) cylindrical tissue must line the layers of the sac with direct connection between the tunica albuginea and sac wall; and 4) evidence of the amniotic cavity connection to the ovarian follicle or corpus luteum. These were replaced by Otto Spiegelbergs criteria in 1878, which have been used into the 20th century with additions and modifications.Up to 1845, about 80 cases of ovarian pregnancy were proposed. With Mayers 1845 denial that ovarian pregnancy could exist, physicians began taking more care in their descriptions and analysis of cases. Though numerous cases were evaluated, some failed to provide microscopic evidence and others failed to show the necessary histological changes of pregnancy, or failed on one or more of the criteria.