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 would be termed a missed abortion only if the diagnosis of incomplete abortion or inevitable abortion was excluded. The condition may present as an anembryonic gestation (empty sac or blighted ovum) or as fetal demise prior to 20 weeks gestation. Before widespread use of ultrasonography, the term missed abortion was given to pregnancies with no uterine growth over a prolonged period of time, typically 6 weeks. Some authorities feel 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 or treated easily, there were reports of disseminated intravascular coagulation (DIC) syndrome associated with prolonged retention of a dead fetus (greater then 6-8 weeks). With early diagnosis and treatment, DIC is extremely rare.

Race: Incidence is similar among all races.

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 exam 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.

WORKUP

¡@

Lab Studies:
¡@

• Quantitative human chorionic gonadotropin

• Quantitative human chorionic gonadotropin (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 followed 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 seen clearly in the uterus, lower-than-expected levels of HCG or progesterone increase the possibility for abnormal pregnancy but are not diagnostic. Therefore, imaging is the study of choice. To make the diagnosis with ultrasound the findings may include, but not be limited to: 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.

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 seen, ectopic pregnancy is ruled out. For naturally conceived pregnancies, the coexistence of ectopic and intrauterine pregnancy is extremely rare (1/30,000). With assisted reproduction technology, however, the coexistence of an ectopic and intrauterine pregnancy should be considered.

• 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 there are ultrasound criteria that 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 will confirm lack of progressive development. In the case of a very early pregnancy where the sac diameter is less than 5-6 mm, it may be better to repeat the study in 10-14 days.

• Serial ultrasound is unnecessary if ultrasound documents 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:
¡@

• Tissue obtained during evacuation should be examined to confirm that products of conception were obtained. More extensive tests, such as chromosomal analysis, are not usually indicated. However in cases of recurrent losses, karyotyping of the parents can be useful.

• Coagulation studies generally are not indicated prior to evacuation. It is important to document Rh status and treat appropriately if Rh negative.

Procedures:
¡@

• Refer to pregnancy termination or spontaneous abortion chapters for information on appropriate procedures.

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, there have been series of patients treated medically. Both mifepristone (RU 486) and misoprostol have been used to empty the uterus. Some series have offered expectant management to those patients with small amounts of tissue in the uterus. While these regimens generally are 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.

MEDICATION

¡@

Although the risk of Rho(D) alloimmunization is minimal following missed abortion, anti-D immune globulin should be administered to women who are Rho(D) negative. This is not necessary if the father is Rho(D) negative.
¡@

Drug Category: Immunoglobulins -- May decrease autoantibody production, and increase solubilization and removal of immune complexes.

FOLLOW-UP

¡@

Further Outpatient Care:
¡@

• Rho(D)-negative patients should receive anti-D immunoglobulin after a missed abortion.

• Emotional support and education are very important. The patient should be assisted through the grieving process.