Implantation of a pregnancy within the scar of a previous cesarean delivery is the rarest of ectopic pregnancy locations. Only 19 cases have been reported in the English medical literature since 1966. If diagnosed early, treatment options are capable of preserving the uterus and subsequent fertility. However, a delay in either diagnosis or treatment can lead to uterine rupture, hysterectomy, and significant maternal morbidity. Although expectant and medical managements have been reported, termination of a cesarean scar pregnancy by laparotomy and hysterotomy, with repair of the accompanying uterine scar dehiscence, may be the best treatment option.
Target Audience: Obstetricians & Gynecologists, Family Physicians
Learning Objectives: After completion of this article, the reader will be able to define the entity of an ectopic pregnancy within a cesarean delivery scar, to list the ultrasound findings used to make the diagnosis of an ectopic pregnancy within a cesarean delivery scar, and to outline a potential management plan for a patient with an ectopic pregnancy within a cesarean delivery scar.
Implantation of a pregnancy within the scar of a previous cesarean delivery is the rarest form of ectopic pregnancy. Including a case treated by the author, a computer MEDLINE and bibliography search has yielded only 19 cases reported in the English language from 1966 through January 2002. The natural history of such a condition is unknown, but uterine scar rupture and hemorrhage, even in the first trimester, seems likely if the pregnancy is allowed to continue, with possible serious maternal morbidity and the possible need for hysterectomy and loss of subsequent fertility. Presented are a review of the reported cases, an analysis of etiologic factors, and an appraisal of treatment options.
Endometrial and myometrial disruption or scarring can predispose to abnormal pregnancy implantation. When the placenta is implanted over the scar of a previous cesarean delivery, the risk of placenta accreta is significantly increased (1–3). Trophoblast adherence or invasion is enhanced when the scant decidualization of the lower uterine segment is impaired further by previous myometrial disruption. Cesarean delivery increases five-fold the incidence of future placenta previa accreta, and the incidence further increases with multiple previous cesarean deliveries (1,2).
Implantation of a pregnancy within the uterine scar of a prior cesarean delivery is different from an intrauterine pregnancy with placenta accreta. Cesarean scar implantation is a gestation completely surrounded by myometrium, and the fibrous tissue of the scar, and separated from the endometrial cavity or fallopian tube. The mechanism that most probably explains scar implantation, like intramural implantation, is invasion of the myometrium through a microscopic tract. With intramural pregnancy, such a tract is believed to develop from the trauma of previous uterine surgery, such as curettage, cesarean delivery, myomectomy, metroplasty, hysteroscopy, and even manual removal of the placenta (1,4,5). The time interval between such trauma and a subsequent pregnancy may impact upon implantation events. Some of the reported cases were diagnosed and treated within a few months of a prior cesarean delivery (6,7), suggesting that incomplete healing of the uterine scar may contribute to scar implantation.
Early diagnosis with ultrasound can offer treatment options capable of avoiding uterine rupture and hemorrhage and, thereby, preserve the uterus. The differential diagnosis between spontaneous abortion in progress, cervico-isthmic pregnancy, and implantation within a cesarean cesarean scar can be difficult. Strict ultrasound imaging criteria must be used to assess the diagnosis of cesarean scar pregnancy. Ultrasound should reveal an empty uterine cavity, an empty cervical canal, development of the gestational sac in the anterior part of the uterine isthmus, and an absence of healthy myometrium between the bladder and sac, this last criterion allowing differentiation from cervico-isthmic implantation (8).