Spontaneous Abortion and Recurrent Pregnancy Loss

What is the definition of an abortion?

An abortion (miscarriage) is defined as a termination or loss of pregnancy before 20 weeks of gestation (as calculated from the date of the last menstrual period) or delivery of a fetus weighing less than 500 g.

What are the different types of abortions?

• Spontaneous (complete or incomplete)

• Induced

• Threatened

• Inevitable

• Missed

• Tubal (can occur with an ectopic pregnancy)

What is the incidence of spontaneous abortions?

Spontaneous abortion is the most common complication of early pregnancy. Approximately 8% to 20% of all clinically recognized pregnancies and as many as 13% to 26% of unrecognized pregnancies end in miscarriage.

When do most clinically recognized spontaneous abortions occur?

Eighty percent of recognized spontaneous abortions occur in the first trimester, and the incidence decreases with increasing gestational age.

What is the most common presentation of spontaneous abortion?

Vaginal bleeding with or without pelvic cramping in the first trimester.

What is the differential diagnosis of vaginal bleeding in the first trimester?

Vaginal bleeding is common in the first trimester, occurring in 20% to 40% of pregnant women; even heavy, prolonged bleeding can be associated with a normal outcome. The differential diagnosis includes the following:

• Threatened abortion

• Ectopic pregnancy

• Vaginal lesions

• Increased friability of the cervix

• Infections (cervicitis, vaginitis, cystitis)

What is the risk of spontaneous abortion in patients who experience first-trimester bleeding?

This outcome affects 25% of women with first trimester bleeding.

What is the most common cause of spontaneous abortion?

Fetal genetic abnormalities are believed to account for as many as 75% of all spontaneous abortions. They are present in 70% of first trimester losses and in 30% of losses in the second trimester.

What are the most common types of chromosomal anomalies found in spontaneously aborted fetuses?

• As a group, autosomal trisomies are the most common (49%). Within this category, trisomy 16 is the most frequent.

• Monosomy X (17%) is the most common single chromosomal abnormality. It is also known as Turner syndrome.

• Polyploidies (19%)

• Structural abnormalities (translocations, inversions) (10%)

What are other causes of spontaneous abortions?

Box 25-1 provides a list of possible causes.