Missed Abortion
INTRODUCTION
Background: Missed abortion refers to the clinical situation in which an intrauterine pregnancy is present but no longer developing normally. The gestation is termed a missed abortion only if the diagnosis of incomplete abortion or inevitable abortion is excluded. Patients with this condition may present with an anembryonic gestation (empty sac or blighted ovum) or with fetal demise prior to 20 weeks’ gestation. Before widespread use of ultrasonography, the term missed abortion was applied to pregnancies with no uterine growth over a prolonged period of time, typically 6 weeks. Some authorities think that more specific descriptive terms should be used; however, the term missed abortion is still widely used among clinicians and is a commonly used indexing term for MEDLINE and other resources.
Pathophysiology: Causes of missed abortion generally are the same as those causing spontaneous abortion or early pregnancy failure. Causes include anembryonic gestation (blighted ovum), fetal chromosomal abnormalities, maternal disease, embryonic anomalies, placental abnormalities, and uterine anomalies. Virtually all spontaneous abortions are preceded by missed abortion. A rare exception is expulsion of a normal pregnancy because of a uterine abnormality.
Frequency:
In the US: Frequency closely correlates with frequency of failed pregnancy in general. In clinically recognized pregnancies, spontaneous abortion occurs in up to 15% of cases. The rate is much higher for preclinical pregnancies. Diagnosis is made much more frequently because of increased use of early ultrasound.
Mortality/Morbidity:
Associated morbidity is similar to that associated with spontaneous abortion and includes bleeding, infection, and retained products of conception.
Previously, before the diagnosis of fetal demise could be made and before the condition could be treated easily, disseminated intravascular coagulation (DIC) syndrome associated with prolonged retention of a dead fetus (>6-8 wk) was reported. With early diagnosis and treatment, DIC is extremely rare.
Race: Incidence is similar among all races.
Age: Pregnancy failure rates increase with age and rise significantly in people older than 40 years.
CLINICAL
History: History is of limited value. Obtaining information about the first diagnosis of pregnancy, any human chorionic gonadotropin (HCG) tests, or abatement of symptoms of pregnancy may help increase the index of suspicion for the diagnosis of missed abortion.
Physical:
Physical examination is of limited value.
A uterus that is small for dates or not increasing in size suggests missed abortion.
Vaginal bleeding is suggestive of missed abortion.
Loss of fetal heart tones or inability to obtain heart tones at the appropriate time leads to suspicion of the diagnosis.
Causes: Causes of missed abortion generally are the same as those causing spontaneous abortion or early pregnancy failure. Causes include anembryonic gestation (blighted ovum), fetal chromosomal abnormalities, maternal disease, embryonic anomalies, placental abnormalities, and uterine anomalies.
DIFFERENTIALS
Ectopic Pregnancy Hydatidiform Mole
Other Problems to be Considered:
Normal intrauterine pregnancyComplete spontaneous abortionIncomplete abortionInevitable abortionMultiple gestation
WORKUP
Lab Studies:
Quantitative human chorionic gonadotropin
Quantitative HCG levels are useful for very early pregnancy evaluation when no sac is visible in the uterus on ultrasound.
If suspicion of ectopic pregnancy exists, levels should be obtained at 48-hour intervals until the discriminatory level is reached. The discriminatory level of HCG is the level at which an intrauterine pregnancy should always be visible on vaginal probe ultrasound. In most institutions, this is about 1500-2000 mIU/mL when standardized to the International Reference Preparation (IRP).
Once the sac is clearly observed in the uterus, lower-than-expected levels of HCG or progesterone increase the possibility for abnormal pregnancy but are not diagnostic. Therefore, imaging studies are the studies of choice. To make the diagnosis with ultrasound the findings may include, but are not limited to, the absence of fetal pole, lack of growth of fetal pole, fetal pole with no evident heart beat, lack of yolk sac at the appropriate gestational age, misshapen yolk sac, or placental separation.
Coagulation studies are generally not indicated prior to evacuation of the uterus.
Documenting Rh status and treating appropriately if the woman is Rh negative is important.
Imaging Studies:
Ultrasound
Once the HCG level has reached the discriminatory level, vaginal ultrasound replaces blood tests as the primary means of evaluation.
If a true intrauterine gestational sac is observed, ectopic pregnancy is ruled out. For naturally conceived pregnancies, the coexistence of ectopic and intrauterine pregnancy is extremely rare (1 out of 30,000 pregnancies). However, with assisted reproduction technology, consider the coexistence of an ectopic and intrauterine pregnancy.
After a sac has been demonstrated in the uterus, the next step is to determine if the pregnancy is normal or abnormal. Transvaginal ultrasound is the best imaging procedure to evaluate intrauterine contents.
While some ultrasound criteria strongly support the diagnosis, most patients and physicians prefer to use repeat ultrasound to confirm that the pregnancy is a missed abortion and not simply an early normal pregnancy. In most cases, a repeat ultrasound in 1 week confirms lack of progressive development. In the case of a very early pregnancy where the sac diameter is less than 5-6 mm, repeating the study in 10-14 days may be more effective.
Serial ultrasound is unnecessary if ultrasound reveals loss of previously documented heart activity.
Ultrasound criteria that strongly suggest missed abortion are sac diameter greater than 16 mm without cardiac activity or fetal pole greater than 4 mm without cardiac activity.
Other Tests:
More extensive tests, such as chromosomal analysis, are not usually indicated. However, in cases of recurrent losses, karyotyping of the parents can be useful.
Procedures:
Refer to Abortion and Surgical Management of Abortion for information on appropriate procedures.
Examine tissue obtained during evacuation to confirm that products of conception were obtained.
Histologic Findings: Histologic findings are similar to that of spontaneous abortion. Varying amounts of placental and/or fetal tissue should be present and are usually reported as products of conception.
TREATMENT
Medical Care: Although missed abortion has been treated surgically in the United States, patients have been treated medically. Both mifepristone (RU 486) and misoprostol have been used to empty the uterus. Some series have offered expectant management to patients with small amounts of tissue in the uterus. While these regimens are generally successful, a number of women require curettage because of retained tissue or bleeding. For now, medical treatment and expectant management are limited to clinical trials or reserved for the patient who refuses surgical treatment. As experience is gathered, these modes of treatment may become more common; however, surgical therapy remains the standard of care at this time. Surgical Care: Missed abortion is usually managed with suction curettage, which is typically performed in an outpatient setting. No large studies compare medical versus surgical treatment.
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