-J. Whitridge Williams (1903)
Following fertilization and fallopian tube transit, the blastocyst normally implants in the endometrial lining of the uterine cavity. Implantation elsewhere is considered ectopic and accounts for 0.5 to 1.5 percent of all irst-trimester pregnancies in the United States (Hoover, 2011; Stulberg, 2014). his small proportion disparately accounts for 3 percent of all pregnancyrelated deaths (Creanga, 2017). Fortunately, urine and serum beta-human chorionic gonadotropin (�-hCG) assays and transvaginal sonography allow earlier diagnosis. As a result, both maternal survival rates and conservation of reproductive capacity are improved.
Nearly 95 percent of ectopic pregnancies are implanted in the various segments of the fallopian tube. hese segments are shown in Chapter 2 (Fig. 2-14, p. 29). he ampulla (70 percent) is the most frequent site, followed by isthmic (12 percent), imbrial (1i1 percent), and interstitial tubal pregnancies (2 percent) (Bouyer, 2002). The remaining 5 percent of nontubal ectopic pregnancies implant in the ovary, peritoneal cavity, cervix, or prior cesarean scar. Occasionally, a multifetal pregnancy contains one conceptus with normal uterine implantation that coexists with one implanted ectopically. he natural incidence of these heterotopic pregnancies approximates 1 per 30,000 pregnancies (Reece, 1983). However, with assisted reproductive technologies (ART), their incidence is 9 in 10,000 pregnancies (Perkins, 2015). Rarely, twin tubal pregnancy with both embryos in the same tube or with one in each tube has been reported (Eze, 2012; Goswami, 2015).
Regardless of location, D-negative women with an ectopic pregnancy who are not sensitized to D-antigen are given IgG anti-D immunoglobulin (American College of Obstetricians and Gynecologists, 2017). In irst-trimester pregnancies, a 50-�g or 300-�g dose is appropriate, whereas a standard 300-�g dose is used for later gestations (Chap. 15, p. 305).
Abnormal fallopian tube anatomy underlies many cases of tubal ectopic pregnancy. Surgeries for a prior tubal pregnancy, for fertility restoration, or for sterilization confer the highest risk. After one previous ectopic pregnancy, the chance of another is increased ivefold (Bhattacharya, 2012). Prior sexually transmitted disease or other tubal infection, which can distort normal tubal anatomy, is another factor. Speciically, one episode of salpingitis can be followed by a subsequent ectopic pregnancy in up to 9 percent of women (Westrom, 1992). Peritubal adhesions subsequent to salpingitis, appendicitis, or endometriosis can also increase chances. Sapingitis isthmica nodosa, which is a condition in which epithelium-lined diverticula extend into a hypertrophied muscularis layer, is another (Bolaji, 2015). Finally, congenital fallopian tube anomalies, especially those secondary to in utero diethylstilbestrol exposure, can predispose (Hoover, 2011).