Abdominal pregnancy

Abdominal pregnancy

William A. Alto

Abdominal pregnancy is a rare and life-threatening variant of ectopic pregnancy. It occurs when the gestational sac is implanted outside the uterus, ovaries and fallopian tubes. Approximately 1 percent of all pregnancies are extrauterine, and 1 to 3 percent of these are peritoneal implantations. The reported incidence of abdominal pregnancy ranges from one in 2,200 to one in 10, 200 pregnancies. [1-5] Although the condition is unusual, any physician who practices obstetrics must be aware of this complication, which is of ten initially misdiagnosed.

CASE REPORT

A 22-year-old primiparous woman was admitted to the hospital in labor at 38 weeks of gestation, with a diagnosis of transverse lie. She had a history of vaginal bleeding in the first trimester but no other complaints. Apart from the transverse lie, physical findings were normal. Fundal height was 38 cm. The cervix was dilated 2 cm but not effaced, and no presenting part was palpated. Because of the transverse lie, the patient was taken to surgery for cesarean delivery. When the abdomen was opened, a gestational sac was found superior to the uterus. The sac was incised and a female infant, weighing 2.6 kg (5 lb, 12 oz) was delivered. The infant had Apgar scores of 2 and 6.

The placenta was attached to the right superior margin of the uterus, the right tube and ovary, and the broad ligament. The placenta was removed because of massive hemorrhage, with blood loss of 3,900 mL. The postoperative course was complicated by a transfusion reaction. The mother and the normal infant were discharged 16 days after delivery. Classification

Abdominal pregnancy can be divided into two types, according to the implantation site and the gestational age.

PRIMARY ABDOMINAL PREGNANCY

Primary peritoneal implantation of the blastocyst is the less common type of abdominal pregnancy (Figure 1). The diagnosis requires the presence of normal fallopian tubes and ovaries, absence of a uteroplacental fistula from a ruptured uterus, and attachment of the conceptus to peritoneal surfaces only. Implantation of the blastocyst in the peritoneum is time-limited, and complete abortion occurs early- before the 12th week of gestation. Surgery (generally performed because of suspected ectopic pregnancy) usually reveals a small, actively hemorrhaging peritoneal implantation site, which is found to contain chorionic villi on microscopic examination. Early implants can occur anywhere within the abdominal cavity, including the liver, spleen and omentum.

SECONDARY ABDOMINAL PREGNANCY

Secondary abdominal pregnancy results when the placenta of a tubal, cornual or uterine pregnancy extends outside its original confines and attaches to other viscera. The placenta remains viable because part of its original blood supply is maintained. The process can be thought of as a partial tubal abortion, with continued placental growth outside the tube (Figure 2). Secondary abdominal pregnancies occur after the 12th week of gestation. Rarely, a tubal pregnancy will completely abort from the site of primary implantation in a fallopian tube and will reimplant in the peritoneum. [2]

Ovarian pregnancy is not considered a true abdominal pregnancy, because the ovary lacks a peritoneal covering. It usually presents early with symptoms resembling those of a tubal pregnancy. Rarely, an ovarian pregnancy goes to term, producing symptoms similar to those of an advanced abdominal pregnancy.

Etiology

Women with a history of salpingitis and peritubal adhesions or scarring are at increased risk of ectopic pregnancy and thus are more likely to have an abdominal pregnancy. Intrauterine devices that prevent intrauterine pregnancy but allow extrauterine pregnancy may also increase the risk. Treatment with gonadotropins to enhance ovulation has been reported to result in abdominal pregnancy [6] as has in vitro fertilization with embryo transfer. [7]

Since fertilization of the ovum frequently occurs within the peritoneal cavity, it is curious that primary intra-abdominal implantation of the zygote does not occur more often. Endometrial tissue is not necessary for implantation of the zygote. If the zygote implants intra-abdominally, there is no decidual formation from the peritoneum to halt trophoblastic invasion of blood vessels. Thus, hemorrhage and abortion of the gestational sac occur early.

Implantation in the endosalpinx provides a more favorable environment for the zygote, and subsequent hemorrhage may not cause complete abortion when the conceptus outgrows its confines. Without surgical intervention, the pregnancy may be absorbed in situ or trophoblastic extension may proceed outside the fallopian tube. Alternatively, the zygote may implant normally in the uterine endometrium and the pregnancy may later become intra-abdominal because of a rent in the uterus, such as a ruptured scar from a cesarean section or a uterine perforation secondary to therapeutic abortion.

Clinical Findings

PRIMARY ABDOMINAL PREGNANCY

Primary abdominal pregnancy presents before the 12th week of gestation and resembles an ectopic tubal pregnancy, except that the fallopian tubes may feel normal during the pelvic examination. Abdominal pain, amenorrhea, vaginal bleeding or spotting, and a positive pregnancy test suggest the diagnosis.

In a study of 12 patients reported by Hallatt and Grove, [2] vaginal bleeding occurred in six patients. Surgery was performed at an average of 38 days of gestation and a hemoperitoneum was found in all patients. The implantation site was within the pelvis in nine patients and was not identified in three patients.

SECONDARY ABDOMINAL PREGNANCY

In contrast to the straightforward presentation of early abdominal pregnancy, the history and clinical findings in secondary cases are often confusing. Recurrent abdominal pain, vomiting in the second and third trimesters, and painful fetal movements are frequent complaints. Multiparous patients may state that “the baby doesn’t feel right.” Often, fetal parts are easily palpated, with the fetus high in the abdomen in a transverse or oblique lie. Occasionally, an enlarged uterus (of ten-to 12-week size) can be located lower in the pelvis, its cervix displaced. Cervical dilation is usually consistent with gestational age, but effacement does not occur.

False labor may occur in secondary abdominal pregnancy, [4] and the false uterus may appear to contract under oxytocin stimulation, misleading an unwary physician. Anemia is occasionally noted late in the first or second trimester; this is due to intra-abdominal bleeding at the time of partial placental separation.

Abdominal pregnancy should be suspected in any case of prolonged missed abortion or unexplained antepartum fetal death. An unusual lie that does not change in position over time is also highly suggestive.

Diagnosis

Early abdominal pregnancies are virtually impossible to identify prior to laparotomy, and less than one-half of advanced abdominal pregnancies are correctly diagnosed before surgery. Often, a prolonged latent stage of “labor” or a failed oxytocin stimulation leads to surgical intervention, and only then is the abdominal pregnancy recognized, many times with disastrous consequences. Interestingly, abdominal pregnancy is associated with an elevated a-fetoprotein level. Sonography may be performed in response to this finding, and an unsuspected abdominal pregnancy may thus be discovered. [8]

Ultrasound scanning is currently the diagnostic procedure of choice, but the findings are often equivocal, especially if the diagnosis is unsuspected. In a review of recent literature, [6,7,9-16] sonographic interpretation was incorrect in the majority of patients. These failures to diagnose abdominal pregnancy occurred even after multiple scans were obtained in most patients. Sonographic findings suggestive of abdominal pregnancy include oligohydramnios, poor placental definition, abnormal fetal lie and an empty uterus low in the pelvis. A thickened gestational sac frequently resembles a gravid uterus and can mislead even the most experienced sonographer. [16]

Magnetic resonance imaging (MRI) has been used successfully in abdominal pregnancies, [9,17] although caution is advised in exposing a first-trimester fetus to MRI. [18] MRI may become the diagnostic procedure of choice for advanced gestations as experience with this technique becomes more extensive.

Abdominal radiographs in the third trimester show the fetus high in the abdomen, overlapping the maternal spine. Fetal parts may be visualized immediately beneath the abdominal wall or intermingled with maternal intestinal gas.

Only a high index of suspicion, coupled with positive clinical signs and a careful review of imaging studies, allows the diagnosis of abdominal pregnancy to be made before surgery.

The Fetus

The status of the fetus in abdominal pregnancy is precarious. The mortality rate varies from 30 to 95 percent. [1,19] Fetal abnormalities are found in 30 to 100 percent of the survivors.[1-3,5] Most of the abnormalities are related to oligohydramnios and to the constricted extrauterine environment, which results in pressure deformities. If the fetus dies and the pregnancy is not diagnosed, mummification may occur or fetal parts may later extrude through a sinus tract into the uterus, the bowel or the abdominal wall. [11]

Management

Once the diagnosis of abdominal pregnancy has been made, immediate surgery is usually advisable, because of the risk to the mother and the improbability of a normal, viable fetus. The ever-present danger of placental separation and catastrophic hemorrhage argues against procrastination. However, if the pregnancy is more advanced than 20 weeks and the mother and the fetus are doing well, it may be reasonable to monitor the pregnancy in the hospital with compatible blood on hand until the fetus reaches a viable stage. [20,21] If the fetus has already died, elective surgery should not be unduly delayed, since hemorrhage, disseminated intravascular coagulation, sepsis or abscess formation may occur.

Since surgery may result in massive, intractable hemorrhage, at least 6 units of blood and an experienced surgical team must be available. Adhesions of the gestational sac to the abdominal wall and viscera are of ten extensive. Once the fetus is delivered, a decision must be made concerning removal of the placenta. Only rarely is the placental implantation limited to the reproductive organs by a single pedicle so that it can be easily removed. [11] Trophoblastic invasion of multiple organs may result in surgically uncontrollable hemorrhage. Frequently the placenta has partially abrupted, with brisk bleeding, since there is no constriction of the hypertrophied, opened blood vessels.

Removal of the placenta and membranes necessitates careful ligation of all bleeders and the use of hemostatic agents. A subtotal hysterectomy may be needed. A medical antishock garment (MAST suit) around the abdomen has been used successfully as a lifesaving measure in cases of intractable hemorrhage from the placental site. It would be reasonable to apply a MAST suit preoperatively, in cases of diagnosed abdominal pregnancy. [22]

If the placenta is not bleeding and is firmly attached (as is usual when the parietal peritoneum, mesentery and bowel are involved), it can be left undisturbed. The umbilical cord is ligated close to the placenta, excess membranes are trimmed away and the abdomen is closed with drainage. Placental involution can be followed by serial sonographic scanning, [9] measurements of human chorionic gonadotropin levels, or gallium scintigrams. [12] However, placental resorption can take months or even years. [9,11]

When the placenta is left in situ, complications such as bowel obstruction secondary to adhesions or intra-abdominal infection with abscess formation occur in about one-half of the patients. [1,3] For this reason, some authors have argued for routine removal of the placenta. [22] Although the problems associated with an abdominally retained placenta may be distressing, they are less potentially disastrous than an ill-advised attempt at removing the placenta.

Prognosis

Maternal mortality can be as high as 20 percent in advanced abdominal pregnancy. [1,3,8] Because the correct diagnosis is usually unsuspected, the physician is not prepared for the massive blood loss that frequently occurs, and adequate resuscitative measures may not be readily available. Extensive adhesions and intractable bleeding make surgery technically difficult, and ureteral and bowel injury are common.

Final Comment

Abdominal pregnancy is a dangerous and often misdiagnosed variant of ectopic pregnancy. As the incidence of pelvic inflammatory disease with subsequent ectopic pregnancies increases, more physicians will encounter abdominal pregnancies. Awareness of the possibility of abdominal pregnancy allows prompt detection and appropriate referral in many cases.

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(Figures omitted)

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