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Early Pregnancy Failure
Providers of medical abortion may encounter patients with abnormal pregnancies. These conditions include early pregnancy failure, ectopic pregnancy, and molar pregnancy. Ultrasonography and hCG testing can be helpful in establishing a diagnosis when the clinical presentation suggests the possibility of these conditions. If TVU is performed before a medical abortion and fails to reveal a gestational sac, the differential diagnosis includes pregnancy too early to be detected by sonography, early pregnancy failure, and ectopic pregnancy.
Early Pregnancy Failure
Early pregnancy failure is characterized by embryonic growth failure. This may be evident at the time of initial ultrasound for medical abortion. Historically, the condition was diagnosed when a large, empty gestational sac was visualized on ultrasound (explaining the older terms "blighted ovum" and "anembryonic pregnancy").
The greater resolution of transvaginal sonography has revealed that early pregnancy failure is a continuum that can initially appear as an abnormal embryo and eventually become an empty sac after reabsorption occurs.
Patients with early pregnancy failure may have bleeding and cramping, or they may have no symptoms. Examination may reveal a uterus smaller than expected for dates; in the case of an actively bleeding patient, products of conception may be evident in the cervical os or vagina.
When no intrauterine pregnancy is detected and the serum ß-hCG level is below the discriminatory zone, the diagnosis could be a failed pregnancy, an ectopic gestation, or an intrauterine pregnancy that is too small to be detected sonographically. A repeat sonogram a few days later or serial ß-hCG levels may be required for diagnosis.
A range of ultrasonographic findings is consistent with early pregnancy failure: a mean gestational sac diameter ≥ 8 mm with no visible yolk sac,42,43 a gestational sac with a mean diameter ≥ 16 mm with no embryo,32 and an embryo with a length > 5 mm with no visible cardiac activity.42,44-46 Confirmation of the diagnosis by repeat ultrasonography a few days later or by serial ß-hCG level is prudent when the patient has any doubts about terminating the pregnancy.
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The risk factors for ectopic pregnancy include a history of ectopic pregnancy, pelvic inflammatory disease, tubal surgery, current use of an intrauterine device, and assisted reproductive technology. A study of surgical abortion patients published in 1997 reported an ectopic pregnancy rate of 6.7 per 1,000 among women seeking surgical abortion at < 6 weeks.47
Patients with ectopic pregnancy may report some abnormal bleeding since their last menstrual period. Another common symptom is unilateral pelvic pain of gradual or sudden onset, which may be mild or severe. Some patients may be completely asymptomatic. The uterus is typically smaller than expected based on LMP, and an adnexal mass or tenderness may be detected on pelvic examination.
The discriminatory level can help narrow the diagnostic possibilities. When the serum ß-hCG level is below the discriminatory level and no intrauterine pregnancy is detected on ultrasound, the differential diagnosis includes an ectopic gestation, a failed pregnancy, or an intrauterine pregnancy too small to be detected sonographically. Conversely, if the ß-hCG concentration exceeds the discriminatory level and no intrauterine pregnancy is seen on ultrasound, then an ectopic pregnancy should be considered present until proven otherwise.29
Suspicion of an ectopic pregnancy warrants examination by an experienced sonographer. Because spontaneous heterotopic pregnancy
of an intrauterine gestational sac
essentially excludes the diagnosis of ectopic pregnancy. Conversely, visualization of an extrauterine yolk sac or embryo
with cardiac activity is pathognomonic for the diagnosis of ectopic pregnancy. However, these findings are detected with transvaginal ultrasonography in only about 15% to 29% of tubal pregnancies.31,48-52
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After reading this section, you should be able to answer the following question:
Which factors increase the risk for molar pregnancy?
Hydatidiform mole, also known as a "molar pregnancy," results from genetic abnormalities. Molar pregnancies are the benign end of a spectrum of trophoblastic neoplasia that includes invasive moles and choriocarcinoma. The prevalence in the United States is approximately 1 per 600 induced abortions.48 Risk factors include extremes of reproductive age, low socioeconomic status, and a history of similar abnormal gestations.54
Abnormal bleeding and nausea or vomiting are the typical symptoms. The uterus may feel larger than expected for dates. Serum ß-hCG levels can aid in this diagnosis, as levels of this hormone are often markedly elevated (> 330,000 mIU/mL). In the late first trimester, complete moles exhibit a classic "snowstorm" or "grape-like" sonographic pattern.
Unlike the situation in later pregnancy, the sonographic appearance in early pregnancy may be indistinguishable from that of pregnancy failure. Molar pregnancy is not generally diagnosable in early pregnancy based on ultrasound findings alone; clinical guidance is required.
When this disorder is diagnosed during the medical abortion screening process, the clinician should explain the problem to the patient and arrange for appropriate treatment. Treatment should include prompt surgical evacuation of the uterus, examination of the contents by a pathologist to detect possible malignancy, and close follow-up for 6 - 12 months to detect recurrences or progression to gestational trophoblastic disease or development of choriocarcinoma.
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