Incidence, risk factors, and pathology of ectopic pregnancy

INTRODUCTION

Ectopic pregnancy occurs when the developing blastocyst becomes implanted at a site other than the endometrium of the uterine cavity. The most common extra-uterine location is the fallopian tube, which accounts for 98 percent of all ectopic gestations (picture 1A-B). Management of these pregnancies has changed dramatically over the years [1]. The guiding principle has become a conservative approach that attempts to save the tube, rather than salpingectomy. However, it is important to remember that hemorrhage from ectopic pregnancy is still the leading cause of pregnancy related maternal death in the first trimester and accounts for 4 to 10 percent of all pregnancy related deaths, despite improved diagnostic methods leading to earlier detection and treatment [2,3].

The incidence, risk factors, and pathology of ectopic pregnancy will be reviewed here. The clinical presentation, diagnosis, and treatment (medical and surgical) of this disorder are discussed separately. (See "Clinical manifestations, diagnosis, and management of ectopic pregnancy" and "Methotrexate treatment of tubal and interstitial ectopic pregnancy" and "Surgical treatment of ectopic pregnancy and prognosis for subsequent fertility".)

INCIDENCE AND EPIDEMIOLOGY

The prevalence of ectopic pregnancy among women who go to an emergency department with first trimester bleeding, pain, or both ranges from six to 16 percent [4]. The overall incidence of ectopic pregnancy increased during the mid twentieth century, plateauing at approximately almost 20 per 1000 pregnancies in the early 1990s, the last time national data were reported by the Centers for Disease Control [2]. This rising incidence is strongly associated with an increased incidence of pelvic inflammatory disease [5].

The current incidence of ectopic pregnancy is difficult to estimate from available data (hospitalizations, insurance billing records) because inpatient hospital treatment of ectopic pregnancy has decreased and multiple health care visits for a single ectopic pregnancy have increased [6]. Furthermore, since the incidence is expressed as the number of ectopic pregnancies/1000 pregnancies, the denominator is difficult to determine accurately since early pregnancy failures that do not result in delivery or hospitalization are often not counted.

Ectopic pregnancy occurs with some seasonal variation and is most common in June and December [7]. The reason is unclear; the authors postulated that reproduction is seasonal, depends on photoperiod and temperature, and varies with different latitudes. Therefore, depending on the location of the investigation, ectopic pregnancy may show different seasonal rhythmicities. An altered maturation of the follicle and oocyte may negatively influence reproductive outcome in the transition between two reproductive steady states of high and low overall fecundity.