Recurrent Abortion

General Considerations

Recurrent abortion is defined as 3 or more consecutive pregnancy losses before 20 weeks gestation, each with a fetus weighing less than 500 g. Approximately .4-1% of women are habitual aborters. Recurrence risks are difficult to quantify and studies are conflicting. Although there is an increased risk of abortion after a previous abortion, no generally accepted recurrence risks exist (Table 14-1). The incidence of clinically-evident abortion when there is no previous history is approximately 15%. This increases to 25-50% when there have been 3 or more miscarriages.

The recurrence risk is higher if the embryo or fetus has a normal karyotype. It may be that maternal causes are responsible for this higher recurrence risk when the karyotype of the abortus is normal.

Despite these conflicting reports, the prognosis following repeated losses is good, with most couples having an approximately 60% chance of a viable pregnancy.

Etiology & Treatment

Chromosomal abnormalities and uterine malformations have been shown to play a role in repetitive miscarriages. Other causes, including hormonal abnormalities, infection, systemic disease, environmental agents, and/or immunologic factors may also play a role. Table 14-2 summarizes a diagnostic work-up for recurrent abortion.

A. Genetic Error

As described previously, there is a 50-60% incidence of abnormal karyotype in first-trimester spontaneous abortions. Possible causes of genetic errors include balanced rearrangements of parental chromosomes such as translocations, found in approximately 2-5% of patients with repetitive abortions.

A careful reproductive history and pedigree should be taken for both partners, and karyotype screening should be performed. It is also useful to know the karyotype of aborted material. If the defect is paternal, artificial insemination is available. For a maternal defect, a donor egg may be fertilized by the husband's sperm. Preimplantation diagnosis is also an option. With this technique, a probe is made for the translocated region. Typically an embryo is allowed to reach the 8-cell stage. A few cells are aspirated and the probe is added. If no translocation is identified in the embryo, it is implanted in the uterus. Table 14-2 details possible therapies for recurrent abortion.

B. Uterine Abnormalities

Anatomic abnormalities were the first described causes of habitual abortion and account for up to 15% of recurrent pregnancy losses. Defects include congenital uterine anomalies, cervical incompetence, submucous leiomyomas, abnormalities due to diethylstilbestrol exposure in utero, and Asherman's syndrome. A major difficulty in counseling couples is that approximately 50% of women with uterine defects have no reproductive problem. Unicornuate and bicornuate uteri each account for approximately one-third of spontaneous abortions due to anatomic abnormalities, and septate uteri account for another 20-25%. Submucous leiomyomas are responsible for a much smaller percentage of repeated losses. Generally, losses from anatomic abnormalities occur in the second trimester. Interference with implantation, lack of an adequate blood supply, or growth restriction are possible mechanisms for recurrent loss.