The blastocyst normally implants in the endometrial lining of the uterine cavity. Implantation anywhere else is considered an ectopic pregnancy. It is derived from the Greek ektopos—out of place. According to the American College of Obstetricians and Gynecologists (2008), 2 percent of all first-trimester pregnancies in the United States are ectopic, and these account for 6 percent of all pregnancy-related deaths. The risk of death from an extrauterine pregnancy is greater than that for pregnancy that either results in a live birth or is intentionally terminated. Moreover, the chance for a subsequent successful pregnancy is reduced after an ectopic pregnancy. With earlier diagnosis, however, both maternal survival and conservation of reproductive capacity are enhanced.
Nearly 95 percent of ectopic pregnancies are implanted in the various segments of the fallopian tubes (Fig. 10-1). Of these, most are ampullary implantations. The remaining 5 percent implant in the ovary, peritoneal cavity, or within the cervix. More recently, cesarean scar pregnancies are reported to be more common than in the past. Occasionally, and usually with assisted reproductive technologies (ART), multifetal pregnancies implant simultaneously with either both ectopic, or one ectopic and the other intrauterine.
Sites of implantation of 1800 ectopic pregnancies from a 10-year population-based study. (Data from Callen, 2000; Bouyer and colleagues, 2003.)
Prior tubal damage, either from a previous ectopic pregnancy or from tubal surgery to relieve infertility or for sterilization, confers the highest risk for ectopic pregnancy (Table 10-1). After one previous ectopic pregnancy, the chance of another is approximately 10 percent (Ankum and colleagues, 1996; Skjeldestad and co-workers, 1998). Infertility, per se, as well as the use of ART to overcome it, is associated with substantively increased risks for ectopic pregnancy (Clayton and colleagues, 2006). The Society for Assisted Reproductive Technology and the American Society for Reproductive Medicine (2007) reported outcomes from more than 108,000 cycles performed in 2001. Ectopic pregnancy rates were 4.3 percent following zygote intrafallopian transfer (ZIFT) but only 1.8 percent with in vitro fertilization (IVF). And “atypical” implantations—cornual, abdominal, cervical, ovarian, and heterotopic pregnancy—are more common following ART procedures. Prior tubal infection or other sexually transmitted diseases are also common risk factors. And so is smoking, which may be a surrogate marker for these infections because of high-risk behavior (Saraiya and co-workers, 1998). Peritubal adhesions subsequent to salpingitis, postabortal or puerperal infection, appendicitis, or endometriosis may increase the risk for tubal pregnancy. One episode of salpingitis can be followed by a subsequent ectopic pregnancy in up to 9 percent of women (Centers for Disease Control and Prevention, 2007).
Table 10-1. Some Reported Risk Factors for Ectopic Pregnancy