Abdominal pregnancy

Abdominal pregnancy (AP) is defined as implantation  of a pregnancy  outside the uterine cavity in the peritoneal cavity, exclusive of tubal, ovarian, or broad ligament locations¹.

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Abdominal ectopic pregnancy, abdominal pregnancy.

Abdominal pregnancy accounts for 1% of all ectopic pregnancies with an estimated incidence 1 in 10.000 live births¹.

There have been several theories about the pathophysiology of abdominal pregnancy. In 1958, Cavanagh postulated that fertilization may occur in the posterior cul-de-sac where sperm is known to accumulate and that an ovum could lay there as a result of the dependent flow of peritoneal fluid². Iwama et al hypothesized that the retroperitoneal pregnancy would occur because of migration of the embryo from the female reproductive organs to the retroperitoneal space by travelling along lymphatic channels³.

Abdominal pregnancy is classified as primary or secondary based on the pathophysiological  mechanism. Most abdominal pregnancies are the secondary type. In primary abdominal pregnancy, the fertilized ovum implants directly on the peritoneal surface. Secondary abdominal pregnancies occur when the conception is extruded from the female reproductive organ (most commonly from the  tube) and secondarily implanted in the abdominal cavity This classification may not make a difference to management of the condition and thus is of limited clinical value.

Abdominal pregnancy can also be classified as early or late based on the gestational age at the time of diagnosis. Early abdominal preganancy is diagnosed at or before 20 weeks of gestation, while late (advanced) abdominal pregnancy is diagnosed after 20 weeks of gestation.

Implantation can occur anywhere on the peritoneal surface or abdominal viscera such as: uterine serosa, pouch of Douglas, omentum, bowel and mesentery, mesosalpinx, the peritoneum of the pelvic and the abdominal walls,  liver, spleen...  The most common implantation sites are recto-uterine and vesico-uterine pouches (24.3%), uterine and tubal serosa (23.9%)⁴.

The trophoblast may also invade the maternal abdominal organs, potentially causing heavy bleeding or organ rupture.

Risk factors for abdominal pregnancy are similar to risks described for other ectopic pregnancies: previous ectopic pregnancy, tubal surgeries/rupture, endometriosis, and pelvic inflammatory disease… No specific risk factors were particularly associated with abdominal pregnancy.

Recurrence risk of abdominal pregnancy is rare.

The clinical presentation is variable. Symptoms are not specific and can overlap with those of other ectopic pregnancies. Lower abdominal pain is one of the most consistent findings and the localizing pain may be related to the site of implantation. In advanced abdominal pregnancy, pain during fetal movements, palpation of fetal parts under the maternal abdominal wall and fetal malpresentations have been reported.

A suboptimal rise in serial human chorionic gonadotropin (ß-hCG) allows to suggest the diagnosis of an ectopic pregnancy but does not help to confirm the diagnosis of an abdominal pregnancy.

Ultrasound is the tool of choice for abdominal pregnancy. The diagnosis of an early abdominal pregnancy is challenging, it does not always allow to distinguish an abdominal pregnancy from other types of extrauterine pregnancies.

Ultrasound features were suggested for the diagnosis of an abdominal pregnancy by Allibone et al: (1) fetus outside the uterus, (2) failure to see a uterine wall between the fetus and the urinary bladder, (3) close approximation of fetal parts and maternal abdominal wall, (4) eccentric position of fetus, (5) placenta outside the uterine cavity, and (6) visualization of the placenta immediately adjacent to the fetal chest and head with no amniotic fluid⁵.

Magnetic resonance imaging (MRI) is helpful especially in the advanced stage. MRI is not only useful to establish the diagnosis of abdominal pregnancy but can also delineate the location and relationship of  the placenta to its adjacent organs and clarify vascular supply. Therefore, MRI is usually indicated when an abdominal pregnancy is diagnosed in an advanced stage to help with preoperative planning and prediction of potential complications during or after medical or surgical treatment.

Despite advanced imaging modalities, only 20–40% abdominal pregnancies are diagnosed preoperatively⁴.

When the implantation site is in the pelvic region and in the early stage, it is difficult to distinguish abdominal pregnancy from tubal ectopic pregnancy. It is not uncommon that an abdominal pregnancy is diagnosed preoperatively as a tubal pregnancy. Tubal pregnancy tends to be located laterally to the uterus whereas abdominal pregnancy is often seen in the pouch of Douglas. Moreover, tubal pregnancy rarely goes beyond 10 weeks of gestational age without rupture and is movable compared with abdominal pregnancy.

Another differential diagnosis is pregnancy in rudimentary horn pregnancy. The ultrasonographic criteria supporting for the diagnosis of a rudimentary horn pregnancy is the presence of myometrial tissue around the gestational sac which is absent in abdominal pregnancy. However, it is not easy to identify the myometrium in advanced stages. MRI can confirm lack of myometrium around an abdominal pregnancy

Ectopic pregnancy is still a significant source of maternal morbidity and mortality. Early diagnosis is a crucial step in preventing unexpected complications. Despite of the advances in diagnostic imaging methods, the diagnosis of ectopic pregnancy remains challenging, especially when the implantation occurs in unusual locations like abdominal pregnancy. Transvaginal sonography of the pelvis remains the primary imaging technique in the evaluation of an abdominal ectopic pregnancy. When transvaginal examination can not determine a pregnancy, a thorough transabdominal examination must be done to look for the rarer locations of abdominal pregnancy. 

If the location of the pregnancy is still uncertain, MRI scan may help to confirm the diagnosis.

Ectopic pregnancy is the leading cause of maternal morbidity and mortality during the first trimester. Abdominal pregnancies have high mortality rate because such pregnancies typically implant on highly vascularized surfaces, and can separate at any time during the gestation, resulting in heavy blood loss. Mortality rates of abdominal pregnancy are 7.7 times higher than in tubal pregnancy, and 89.8 times higher than in intrauterine pregnancy⁷. However, full-term abdominal pregnancies with live births have been reported in the literature⁸.

There is no optimal treatment for abdominal pregnancy. Management method depends on maternal hemodynamic status and gestational age at diagnosis. Medical management is usually opted for  in early abdominal pregnancy and in pregnancies where surgery may lead to potentially severe bleeding. The most common complication of advanced abdominal pregnancy is life-threatening bleeding from the placental site, which usually happens during the laparotomy. Therefore, the general recommendation is to leave the placenta in situ and monitor the patient’s level of human chorionic gonadotropin. Expectant management to attain fetal viability despite maternal life-threatening risk has been described by several authors in literature when couples have refused for termination of pregnancy⁹.

1. embryo transfer: a case report and systematic review Reprod. Biol. Endocrinol., 14 (2016), p. 69
2. Cavanagh D. Primary Primary peritoneal pregnancy. Am J Obstet Gynecol 1958;76:523–32.
3. Iwama H, Tsutsumi S, Igarashi H, Takahashi K, Nakahara K, Kurachi H. A case of retroperitoneal ectopic pregnancy following IVF-ET in a patient with previous bilateral salpingectomy. Am J Perinatol 2008; 25:33–6.
4. P. Aaron, H. David, F.M. Everett. Early abdominal ectopic pregnancies: a systematic review of the literature. Gynecol. Obstet. Invest., 74 (2012), pp. 249-260.
5. Allibone GW, Fagan CJ, Porter SC. The sonographic features of intra-abdominal pregnancy. J Clin Ultrasound 1981; 9:383–7.
6. A. Nilesh, O. Funlayo Early abdominal ectopic pregnancy: challenges, update and review of current management.Obstet. Gynecol., 16 (2014), pp. 193-198
7. Atrash HK, Friede A, Hogue CJR. Abdominal pregnancy in the United States: frequency and maternal mortality. Obstet Gynecol 1987; 69:333–7
8. Marcellin L, Ménard S, Lamau MC, Mignon A, Aubelle MS, Grangé G, Gofnet F (2014) Conservative management of an advanced abdominal pregnancy at 22 weeks. AJP Rep 4(1):55
9. Rohilla M, Joshi B, Jain V, Neetimala, Gainder S. Advanced abdominal pregnancy: a search for consensus. Review of literature along with case report. Arch Gynecol Obstet. 2018 Jul;298(1):1-8. doi: 10.1007/s00404-018-4743-3. Epub 2018 Mar 17. PMID: 29550945.

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