A Perinatal Pathology View of Preterm Labor

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Utility of Clinical Indicators

Biochemical assays for human chorionic gonadotropin, cytokines (eg, interleukin-6 and tumor necrosis factor alpha), maternal serum alpha-fetoprotein, placental alkaline phosphatase, fetal fibronectin, matrix metalloproteinases, estrogens, and corticotropin-releasing hormone have all been proposed and studied as potential markers of impending preterm delivery. Because of the marked heterogeneous etiology and pathogenesis of preterm delivery, however, it is clear that multiple biomarkers, coupled with other pertinent clinical and sociodemographic data, are required to get a sufficient specificity, sensitivity, and positive predictive value.[9] Development of better assays, along with improved sonography techniques, may allow better elucidation of pathogenetic mechanisms.

Precocious cervical changes at the internal os, as viewed by transvaginal ultrasonography, have been suggested as a sign of preterm labor or premature rupture of the membranes, but the actual mechanism behind these changes is not known.[10] Cervical shortening has been investigated in relation to placental histologic features. In a recent study, [11] investigators found that ultrasonographic evidence of cervical shortening (down to < 2 cm) between 15 and 24 weeks gestation in women at risk of pregnancy loss or spontaneous preterm birth significantly correlated with the presence and extent of acute inflammatory processes in their placentas. Those women with no evidence of cervical shortening were significantly more likely to have decidual vascular lesions.

It again becomes clear that preterm birth most likely has a multifactorial etiology; in addition to the heterogeneity of clinical presentations, there is a range of uteroplacental tissue lesions seen in different combinations in prematurity. One example of the clinical manifestations of an underlying pathology may be seen in a data set of singleton, very early, non-preeclamptic preterm deliveries (22-32 weeks), where mean maternal admission blood pressure was directly related to the severity of placental vascular pathology [the presence/extent of uteroplacental vascular lesions (P = .01) and lesions of intraplacental vaso-occlusion (P = .04)].[12]

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