Miscarriage and Its Associations

Stephen Brown, M.D.

Disclosures

Semin Reprod Med. 2008;26(5):391-400. 

In This Article

Anatomic Abnormalities

Congenital

Uterine abnormalities have long been reported to be associated with an increase in poor reproductive outcomes. Much of the data supporting these associations are from comparisons of loss rates in populations with and without these abnormalities and from nonrandomized studies that have shown decreased loss rates after surgical treatment. Clearly, there are also many examples of women with various types of anomalies and successful reproductive outcome, and this has led to some debate about which types of abnormalities are most likely to cause problems and which should be operated upon.[22] It is generally understood that women with recurrent second-trimester loss need to be evaluated for uterine anomalies, and because this situation occurs relatively rarely, it is not difficult to undertake. A more frequent and difficult question relates to the role of uterine anomalies in first-trimester loss. A recent study showed that, whereas uterine anomalies are fairly common in women without a poor reproductive history, their incidence is about threefold higher in women with a history of recurrent first-trimester miscarriage. Women with a miscarriage history also had more severe distortion of their uterine cavities compared with the "low-risk population," adding to the argument that congenital uterine anomalies may indeed contribute to recurrent miscarriages.[23a] There are several reports in which women with recurrent loss and a uterine anomaly (most commonly septate uterus) were found to have improvement after surgery,[23b] and this has been used as evidence that septate uterus causes first-trimester loss. It is not possible to conclude that surgery is effective until a randomized prospective trial is reported; nonetheless, such treatment seems reasonable in women with several late first-trimester losses.

Leiomyomata

Uterine fibroids are very common and have been cited as a cause of miscarriage. Some plausible mechanisms by which fibroids might cause miscarriage include (1) disruption of implantation and development of the fetal blood supply, (2) rapid growth and degeneration with release of cytokines, and (3) occupation of space for the fetus to grow. All of these proposed mechanisms are consistent with the observation that submucosal fibroids appear to be associated with the highest early loss rates. Given the fact that miscarriage and leiomyomata are both common, it is not surprising that both occur in the same patient. Determining whether the presence of fibroids is actually associated with an increase risk of miscarriage is more complex, and surprisingly few studies attempting to document such an association have been published. Nonetheless, there are several studies that show an increased risk of miscarriage when ultrasonographically detected fibroids are present. In one prospective study, 143 women with fibroids detected prior to 13 weeks of pregnancy were compared with 715 controls.[24] The authors found that the overall rate of miscarriage was twice as high in women with fibroids and that the likelihood of miscarriage increased as the number and size of fibroids increased. Women with four or more fibroids had a loss rate of ∼27%, which is remarkably high considering that a documented fetal heart rate was an inclusion requirement for the study. Another (retrospective) study assessed women in the second trimester and found that the presence of fibroids was associated with a very marked increased risk of loss.[25] Thus, although the literature is not large, there is reason to believe that the presence of uterine fibroids is likely to be an independent risk factor for loss of sonographically viable pregnancies.

Not surprisingly, surgery has been reported as a treatment for miscarriage;[26] however, most studies seeking to assess the utility of myomectomy as a treatment for miscarriage have had significant methodological problems. Surgical treatment should probably be reserved for those women with several fibroids that impinge on the uterine cavity and have lost several, ostensibly viable, pregnancies.

Polyps and Adhesions

With the dramatic increases in the use of assisted reproductive technologies as well as the technical improvements in ultrasound, many women are having extensive evaluations of their reproductive organs, and as a result, uterine abnormalities such as polyps and adhesions are frequently noted. The data on reproductive outcomes of these women are being reported but may not be comparable with fertile women with incidental findings of these uterine abnormalities. There is some evidence that size of a polyp, especially as it approaches 2 cm, may be associated with increased miscarriage. Hysteroscopic polypectomy carries little risk and may improve reproductive outcome in cases of polyps 2 cm or greater in women undergoing assisted reproductive technology.[27] Although textbooks refer to an association of uterine adhesions and miscarriage, there are no recent observational studies or well-designed therapeutic studies to support this. As with the other uterine abnormalities reviewed, it is plausible that significant restrictions on cavity size or implantation on poorly vascularized scar tissue could well be a mechanism by which adhesions lead to poor reproductive outcomes.

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