Spontaneous Pregnancy Loss (Abortion, Miscarriage)

Introduction

• Description: In the first trimester, the terms miscarriage, spontaneous abortion, and early pregnancy loss are used interchangeably. Abortion is the loss or failure of early pregnancy (generally first trimester) in several forms: complete, incomplete, inevitable, missed, septic, and threatened. Except for threatened abortions, these losses generally involve a nonviable pregnancy. A complete abortion is the termination of a pregnancy before the age of viability, typically defined as occurring at less than 20 weeks from the first day of the last normal menstrual period or involving a fetus with a weight less than 500 g. Most complete abortions generally occur before 6 weeks or after 14 weeks of gestation. An incomplete abortion is the spontaneous passage of some, but not all, of the products of conception, associated with uniform pregnancy loss. A pregnancy in which the rupture of the membranes and/or cervical dilation occurs during the first weeks of pregnancy is labeled as an inevitable abortion. Uterine contractions typically follow, ending in the spontaneous loss of the pregnancy for most patients. A missed abortion is the retention of a failed intrauterine pregnancy for an extended period; however, with ultrasonographic studies, this can often be detected significantly sooner than it could be on clinical grounds alone. A septic abortion is a variant of an incomplete abortion in which the uterus and its contents are infected. A threatened abortion is a pregnancy that is at a risk for some reason. Most often, this applies to any pregnancy wherein vaginal bleeding or uterine cramping occurs, but no cervical changes have occurred. Not all of these cases end in the loss of the pregnancy.

• Prevalence: Estimates for the frequency of complete abortions are as high as 50%–60% of all conceptions and between 10% and 15% of known pregnancies. Of pregnant women hospitalized for bleeding, 60% have an incomplete abortion. Less than 2% of fetal losses are missed abortions. Septic abortions occur in 0.4–0.6 of 100,000 spontaneous pregnancy losses. Threatened abortions occur in 30%–40% of pregnant women. About 80% of all pregnancy losses occur in the first trimester.

• Predominant Age: Reproductive.

• Genetics: In about 50% of conceptuses lost, chromosomal abnormalities are present. Some maternal chromosomal abnormalities are associated with reduced or absent fertility and increased risk of fetal loss (eg, translocations).

Etiology and Pathogenesis

• Causes: Endocrine abnormalities (25%–50%)—hyperandrogenism, in utero diethylstilbestrol (DES) exposure (rare now), luteal phase defect, and thyroid disease. Genetic factors (10%–70%)—balanced translocation/carrier state, nondisjunction, trisomy (40%–50%, trisomy 16 most common, any possible except trisomy 1), monosomy X (15%–25%), and triploidy (15%), tetraploidy (5%). Reproductive tract abnormalities (6%–12%)—abnormality of placentation, bicornuate or unicornuate uterus, incompetent cervix, intrauterine adhesions (Asherman syndrome), leiomyomata uteri (submucous), and septate uterus. Infection— Mycoplasma hominis, syphilis, toxoplasmosis, Ureaplasma ureolyticus, and possibly chlamydia and herpes. Systemic disease—chronic cardiovascular disease, chronic renal disease, diabetes mellitus, and systemic lupus erythematosus/lupus anticoagulant. Environmental factors—alcohol, anesthetic gases, drug use, radiation, smoking, and toxins. Other factors—advanced maternal age, delayed fertilization (old egg), and trauma.

• Risk Factors: Increasing parity, increasing maternal age (80% loss risk for age 40–45 years), increasing paternal age, prior pregnancy loss, a short interval between pregnancies, excessive caffeine consumption (≥6 cups of coffee per day). Retention of tissue after pregnancy loss increases the risk of a septic abortion.

Signs and Symptoms

• General—vaginal bleeding (may be bright red to dark in color)

  • Abdominal cramping (frequently rhythmic, accompanied by pelvic or low back pressure)

  • Passage of tissue (complete and incomplete abortion)

  • Cervical dilation (typical of all types of abortion except missed and threatened)

  • Cervical dilation with tissue visible at the cervical os (diagnostic of either incomplete or inevitable abortion)

• Missed abortion—decreased or minimal uterine growth early in pregnancy

  • Vaginal bleeding that changes to a dark brown discharge that continues

  • Loss of early symptoms of pregnancy, such as breast fullness or morning sickness

  • Disseminated intravascular coagulopathy (DIC) can occur when an intrauterine fetal demise in the second trimester has been retained beyond 6 weeks after the death of the fetus (rare)

• Septic abortion—severe hemorrhage (vaginal)

  • Midline lower abdominal pain

  • Uterine and perimetric tenderness

  • Bacteremia

  • Septic shock

  • Renal failure

• Threatened abortion—implantation bleeding

Diagnostic Approach