Abdominal Pregnancy (Extrauterine Pregnancy)

GENESIS

Ectopic pregnancy , defined as the implantation of a fertilized ovum outside the uterus, occurs most commonly in the fallopian tube (95.5% of all ectopic pregnancies), with 70% implanting in the ampulla, 12% in the isthmus, 11% in the fimbrial end, 2% in the interstitial region, and 3% ovarian ( Fig. 48.1 A ). Only 1.3% of ectopic pregnancies are abdominal, occurring with direct implantation onto the peritoneal surface (see Fig. 48.1B ). Abdominal pregnancies are classified as either primary or secondary to tubal or ovarian pregnancies, which rupture into the peritoneal cavity and reimplant for a second time. Reported sites of implantation have included the posterior cul-de-sac, posterior uterine wall (most commonly), uterine serosa, uterine ligaments, omentum, almost all intraperitoneal organs, diaphragm, and retroperitoneal space. Abdominal pain in different locations is the most common presenting symptom. The incidence of ectopic pregnancies increased from 4.5 per 1000 pregnancies in 1970 to 19.7 per 1000 pregnancies in 1992, with this increase attributed to the increasing use of assisted reproductive techniques. Risk factors for ectopic pregnancy include previous Chlamydia trachomatis infection (adjusted odds ratio [aOR]: 3.18), prior ectopic pregnancy (aOR: 2.72), previous adnexal surgery (aOR: 2.09), previous infertility (aOR: 2.18), use of an intrauterine device (aOR: 1.72), previous appendectomy (aOR: 1.64), use of in vitro fertilization, pelvic inflammatory disease, multiple sexual partners, endometriosis, and cigarette smoking. The risk of ectopic pregnancy increased with a prior ectopic pregnancy, prior tubal ligation, use of intrauterine device (IUD), and prior pelvic/abdominal surgery in a sample of 150 Iranian women with ectopic pregnancy compared with 300 controls. A case-control study in women with planned pregnancy included 900 women diagnosed with ectopic pregnancy (case group) and 889 women with intrauterine pregnancy as the control group. Ectopic pregnancy was associated with previous adnexal surgery, uncertainty of previous pelvic inflammatory disease, and positive serum C. trachomatis immunoglobulin G antibody. A history of infertility including tubal infertility, nontubal infertility, and in vitro fertilization treatment was correlated with the risk of ectopic pregnancy in an umbrella review of risk factors prior to conception. Metaanalyses and systematic reviews carried out through June 25, 2021 graded two risk factors as suggestive evidence: C. trachomatis (odds ratio [OR]: 3.03) and smoking (OR: 1.77). Two other risk factors were graded as weak evidence: endometriosis (OR: 2.66) and tubal ligation (OR: 9.3). Currently, the incidence of ectopic pregnancy is 1.3% to 2.4%, with suspicion starting after a positive serum pregnancy test and failure to visualize the intrauterine gestational sac by transvaginal ultrasonography, which is superior to abdominal ultrasonography.

There is usually less early compression and disruption with abdominal pregnancy compared with tubal ectopic pregnancy, and the fetus is more likely to survive. The maternal mortality rate of abdominal pregnancy is seven to eight times higher than that of tubal pregnancy and 90-fold higher than that of intrauterine pregnancy. Most of this increased risk is caused by massive maternal hemorrhage from partial or total placental separation. Clinical presentation is extremely variable, and the maternal mortality rate is approximately 6%. Maternal morbidity includes massive hemorrhage, infection, toxemia, disseminated intravascular coagulation, pulmonary embolism, and formation of a fistula between the amniotic sac and intestine. Some ruptured tubal ectopic pregnancies result in abdominal pregnancies; thus abdominal pregnancy affects about 1 in 6000 to 1 in 10,000 deliveries. A history of pelvic pain along with an abnormal beta human chorionic gonadotropin level should trigger an evaluation for an ectopic pregnancy. The fallopian tube is the most common location for an ectopic pregnancy, and 88% of tubal ectopic pregnancies are diagnosed by absence of a gestational sac and presence of an adnexal mass that is separate from the uterus during transvaginal ultrasound.

Other types of ectopic pregnancy include cornual (an ectopic pregnancy within a malformed uterus), ovarian ( Fig. 48.1A ), cesarean scar, cervical, intraabdominal, and heterotopic pregnancy. Interstitial pregnancy occurs when the gestational sac implants in the myometrial segment of the fallopian tube. Cornual pregnancy refers to the implantation of a blastocyst within the cornua of a bicornuate or septate uterus. An ovarian pregnancy occurs when an ovum is fertilized and retained within the ovary (see Fig. 48.1A ). Cervical pregnancy results from an implantation within the endocervical canal. In a scar pregnancy, implantation takes place within the scar of a prior cesarean section. In an intraabdominal pregnancy, implantation occurs within the intraperitoneal cavity. Heterotopic pregnancy occurs when an intrauterine and an extrauterine pregnancy occurs simultaneously. IUD is a contraceptive method that prevents 99.5% intrauterine implantations, and if implantation occurs with an IUD in place, it is a tubal implantation in 95% of cases and rarely in other places such as the ovary. Cervical heterotopic pregnancy is a very rare event that almost universally results from infertility treatment.

Because most diagnoses of advanced abdominal pregnancy are missed preoperatively, even with the use of sonography, the cornerstones of successful management seem to be quick intraoperative recognition, surgical skill, and ready access to blood products, with meticulous postoperative care and thorough assessment of the newborn. It is usually easier to appreciate an abdominal pregnancy at the end of the first trimester or early in the second trimester, when the pelvic organs are best visualized. The most specific findings to diagnose abdominal pregnancy are the absence of an intrauterine gestational sac combined with a clearly extrauterine gestational sac, fetus, and/or placenta. During the second or third trimester, sonographic findings include the absence of intervening myometrium between amniotic fluid and adjacent maternal pelvic or abdominal viscera, and the inability to establish continuity between the cervical canal and the amniotic cavity. Advanced extrauterine pregnancy is an extremely rare, life-threatening pregnancy complication. Management of such pregnancies presents significant challenges, especially when they have progressed to an advanced stage of fetal viability. With high rates of maternal and fetal mortality associated with this complication, delivery or pregnancy interruption should be expedited following diagnosis. Localization of the placenta and its blood supply is critical to preoperative planning. Because the placentation in advanced abdominal pregnancy is presumed to be inadequate, advanced abdominal pregnancy can be complicated by preeclampsia, which is another condition with high maternal and perinatal morbidity and mortality. After the baby is extracted, because the placenta is implanted in an abnormal site, its removal can result in massive intraoperative bleeding necessitating blood and blood product transfusion and the administration of factor VII to control the bleeding.

Abdominal pregnancies usually arise when a fertilized ovum ruptures from within the fallopian tube and implants within the peritoneal cavity, and only rarely does fertilization of the ovum take place outside the fallopian tube. In other instances, rupture of one horn of a bicornuate uterus can lead to a secondary abdominal pregnancy, and presence of a congenital uterine malformation is a known risk factor for abdominal pregnancy. Cocaine use has also been associated with a 20% increase in the incidence of abdominal pregnancy. Ovarian pregnancies are included within the broader category of extrauterine pregnancies, comprising 0.5% to 1% of all ectopic gestations (see Fig. 48.1A ), and the presence of an IUD is one risk factor. These pregnancies present similarly to ruptured tubal ectopic pregnancy or ruptured hemorrhagic ovarian cyst, with severe hypogastric abdominal pain, irregular vaginal bleeding, and clinical shock in some cases.