Spontaneous Abortion Spontaneous abortion is a pathologic process resulting in unintentional termination of the pregnancy prior to 20 weeks’ gestation. About 8% to 20% of known pregnancies terminate in spontaneous abortion (2,3). About 80% of spontaneous pregnancy losses occur in the first trimester; the incidence decreases with each gestational week (4–6). In women who had one prior spontaneous abortion, the rate of spontaneous abortion in a subsequent pregnancy ranges from 13% to 20%; in women who had three consecutive losses, the rate is 33% (7). Patients should be reassured that, in most cases, spontaneous abortion does not recur. In women less than 36 years of age, when fetal cardiac activity is confirmed by ultrasound, the risk of spontaneous abortion is less than 4.5%. For women older than 36, the risk of spontaneous abortion rises to 10%, and above 40 years may approach 30% (8). Risk factors for spontaneous abortion include increasing maternal age, closely spaced pregnancies (less than 3 to 6 months apart), history of previous spontaneous abortion, maternal diabetes, and maternal smoking during pregnancy (9–13).
Figure 20.1 Common sites of ectopic pregnancy. (Adapted from Seeber BE. Suspected ectopic pregnancy. Obstet Gynecol 2006;107:399–413.)
With pelvic ultrasound, spontaneous abortion can be differentiated into various categories, based on examination findings and ultrasound findings. Missed abortion is defined as a nonviable intrauterine pregnancy in the presence of a closed cervix and little or no abdominal cramping or vaginal bleeding and can be subdivided into anembryonic gestation and embryonic demise. Anembryonic gestation is a pregnancy where the embryo failed to develop and is confirmed
Table 20.1 Potential Causes of Spontaneous Pregnancy Loss
Maternal systemic disease (diabetes mellitus, infection, thrombophilia, etc.)
Maternal alcohol consumption (moderate to high)
Extremes of maternal weight when the mean gestational sac diameter measured by transvaginal ultrasound is greater than 20 mm and no embryonic pole is present. When an embryo is present with crown-rump length greater than 5 mm and no cardiac activity, this is classified as embryonic demise, and the pregnancy is nonviable (14).
Threatened Abortion Threatened abortion is defined as vaginal bleeding before 20 weeks of gestation. It occurs in at least 20% of all pregnancies (15). The distinction from missed or inevitable abortion requires ultrasound documentation of an intrauterine embryo or fetus with cardiac activity. The bleeding is usually light and may be associated with mild lower abdominal or cramping pain. The differential diagnosis in these patients includes consideration of possible cervical polyps, vaginitis, cervical carcinoma, gestational trophoblastic disease, ectopic pregnancy, trauma, and foreign body. On physical examination, the abdomen usually is not tender, and the cervix is closed. Bleeding can be seen coming from the os, and usually there is no cervical motion or adnexal tenderness.