An anembryonic pregnancy is characterized by a gestational sac that forms and grows while an embryo fails to develop. Although the terms anembryonic pregnancy and blighted ovum are synonymous, the latter is falling out of favor for the more descriptive former term. Anembryonic pregnancy constitutes a significant but unknown proportion of miscarriages with the American Pregnancy Association estimating anembryonic pregnancy to constitute half of all first trimester miscarriages. Approximately 15% of all clinically recognized pregnancies end in first-trimester loss with live birth occurring in only 30% of all pregnancies.  A significant proportion of patients with early pregnancy loss(that include anembryonic pregnancies) are unaware of their miscarriage particularly when early pregnancy loss occurs in the early stages of pregnancy.
In the first trimester, the terms early pregnancy loss, miscarriage, or spontaneous abortion are often used interchangeably. Early pregnancy loss is defined as the spontaneous loss of a pregnancy before 13 weeks of gestation.
What is a Miscarriage?
The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) define miscarriage as the loss of a pregnancy before 20 weeks of gestation or the ejection or removal of an embryo or fetus that weighs 500 g or less. This definition is used in the United States; however, it may vary based on State laws.
Biochemical miscarriage is a loss that occurs after a positive urine pregnancy test (hCG) or a raised serum beta-hCG before ultrasound or histological verification and confirmation.
Clinical miscarriage is when ultrasound examination or histologic evidence has confirmed the existence of an intrauterine pregnancy. Clinical miscarriage is classified as early (before 12 weeks of pregnancy) and late (12 weeks to 20 weeks).
The exact etiology for anembryonic pregnancies is difficult to ascertain. The etiological factors for anembryonic pregnancies are generally understood and studied in the broader context of early pregnancy loss (EPL) which includes both embryonic and anembryonic pregnancies. Etiologies include:
Although difficult to definitively establish, anembryonic pregnancy possibly represents half of all miscarriages in the first trimester of pregnancy.  The incidence of early pregnancy loss (before 12 weeks) is estimated to be about 15% of clinically evident conceptions with significant variations in incidence based on patient age. The incidence ranges from 10% in women 20 to 24 years of age to 51% in women 40 to 44 years of age.  A prior history of early pregnancy loss also predisposes a patient to miscarriage. 
The signs and symptoms of an anembryonic pregnancy can potentially mirror those of an ectopic pregnancy. Anembryonic pregnancy is often incidentally noted on an initial first-trimester pregnancy sonogram. If an anembryonic pregnancy progresses to an early pregnancy loss, the patient can present with abdominal cramping and vaginal bleeding. Early pregnancy loss in the setting of an anembryonic pregnancy can be clinically silent.
Clinical signs and symptoms, a pregnancy test, and an ultrasound exam confirm the diagnosis.
A pregnancy test can be obtained using urine or serum hCG levels.
Ultrasound exam (transabdominal or transvaginal) classically demonstrates an empty gestational sac without an embryo.
An anembryonic pregnancy is established on endovaginal ultrasound technique when there is no discernable embryo seen in a gestational sac with a mean sac diameter of ≥25 mm.
Alternatively, an anembryonic pregnancy can be established when there is no embryo on a follow-up endovaginal scan:
The three treatment options for early pregnancy loss include expectant management, medical management, and surgical treatment. Medical management with misoprostol and surgical treatment is considered more effective in the management of anembryonic pregnancy. Ultimately the decision on considering one of these options is based on an informed conversation between a patient and the provider.
The chief obstetric differential diagnosis for an anembryonic pregnancy includes:
Prognosis and successful management of early pregnancy loss depends on a variety of factors including gestation age. Prognosis is generally considered good with all three management options.
Serious complications of treatment are uncommon. Complications can include:
The following represent key points in patient education:
Establishing an anembryonic pregnancy can sometimes b difficult on an ultrasound. Communication with the radiologist relaying hCG lab values and patient presentation can be helpful in avoiding a missed diagnosis of an ectopic pregnancy. The sonographer also plays an important role in accurately evaluating a patient to appropriately exclude an ectopic pregnancy. Patients presenting with complications of either initial presentation or from treatment often present to the emergency department. Interprofessional communication between an emergency department provider and an OB/GYN specialist includes communicating a detailed and thorough history and physical exam. This especially includes signs of sepsis or hemodynamic instability. The role of a mental health professional in following up with patients is also critical in ensuring the appropriate mental health management of a possibly traumatic experience for a patient.
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