Spontaneous Abortion: Etiology

Etiology

INFECTIOUS FACTORS

Infections are an uncommon cause of early spontaneous abortion. Chlamydia trachomatis and Listeria monocytogenes have been associated with spontaneous abortion. Sero-logical evidence supports a role for Mycoplasma hominis and Ureaplasma urealyticum in abortions. Finally, abortion is independently associated with serological evidence of syphilis, human immunodeficiency virus (HIV)-1 infection, and with vaginal colonization with group B streptococci.

ENDOCRINE FACTORS

Thyroid autoantibodies are associated with an increased incidence of spontaneous abortion, even in the absence of clinical hypothyroidism. In women with type 1 diabetes, the degree of metabolic control in early pregnancy is asso-ciated with an increased risk of spontaneous abortion and major congenital malformation.

ENVIRONMENTAL FACTORS

The abortion risk increases in a linear fashion with the number of cigarettes smoked per day. Both spontaneous abortion and fetal anomalies may result from frequent, high doses of alcohol use during the first 8 weeks of preg-nancy. Radiation administered at therapeutic doses to treat cancer may be an abortifacient. It is important to note that exposure to less than 5 rads does not increase the risk for miscarriage.

IMMUNOLOGIC FACTORS

There are a number of genetic disorders of blood coagula-tion that may increase the risk of both arterial and venous thrombosis. Some of the better studied thrombophilias are caused by mutations of the gene for factor V Leiden, pro-thrombin G20210A mutation, antithrombin III, proteins C and S, and methylene tetrahydrofolate reductase (hyper-homocysteinemia). These are most commonly associated with recurrent miscarriage.

UTERINE FACTORS

Large and multiple uterine leiomyomas are common, and they may cause miscarriage. In most instances, their loca-tion is more important than their size, with submucous leiomyomata playing a more significant role than others, presumably because of their effect on implantation. In utero exposure to diethylstilbestrol (DES) has been associated with abnormally shaped uteri as well as cervical incompe-tence and spontaneous abortion. Intrauterine synechiae (Asherman syndrome), a condition that is caused by uterine curettage with subsequent destruction and scarring of the endometrium, may also be a cause of spontaneous abortion