Spontaneous Abortion

Introduction

Essentials of Diagnosis

• Intrauterine pregnancy at less than 20 weeks.
• Low or falling levels of hCG.
• Bleeding, midline cramping pain.
• Open cervical os.
• Complete or partial expulsion of products of conception.

General Considerations

About three-fourths of spontaneous abortions occur before the 16th week; of these, three-fourths occur before the eighth week. Almost 20% of all clinically recognized pregnancies terminate in spontaneous abortion.

More than 60% of spontaneous abortions result from chromosomal defects due to maternal or paternal factors; about 15% appear to be associated with maternal trauma, infections, dietary deficiencies, diabetes mellitus, hypothyroidism, or anatomic malformations. There is no reliable evidence that abortion may be induced by psychic stimuli such as severe fright, grief, anger, or anxiety. In about one-fourth of cases, the cause of abortion cannot be determined. There is no evidence that video display terminals or associated electromagnetic fields are related to an increased risk of spontaneous abortion.

It is important to distinguish women with a history of incompetent cervix from those with more typical early abortion and those with premature labor or rupture of the membranes. Characteristically, incompetent cervix presents as "silent" cervical dilation (ie, with minimal uterine contractions) between 16 and 28 weeks of gestation. Women with incompetent cervix often present with significant cervical dilation (2 cm or more) and minimal symptoms. When the cervix reaches 4 cm or more, active uterine contractions or rupture of the membranes may occur secondary to the degree of cervical dilation. This does not change the primary diagnosis. Factors that predispose to incompetent cervix are a history of incompetent cervix with a previous pregnancy, cervical conization or surgery, cervical injury, DES exposure, and anatomic abnormalities of the cervix. Prior to pregnancy or during the first trimester, there are no methods for determining whether the cervix will eventually be incompetent. After 14-16 weeks, ultrasound may be used to evaluate the internal anatomy of the lower uterine segment and cervix for the funneling and shortening abnormalities consistent with cervical incompetence.

Clinical Findings

A. Symptoms and Signs

1. Threatened abortion
Bleeding or cramping occurs, but the pregnancy continues. The cervix is not dilated.

2. Inevitable abortion
The cervix is dilated and the membranes may be ruptured, but passage of the products of conception has not occurred. Bleeding and cramping persist, and passage of the products of conception is considered inevitable.