Biological Predictors

Biological markers may be collected from maternal blood or urine, cervicovaginal fluid secretions, or amniotic fluid. Maternal blood and vaginal fluids have been the most studied. Table 9-4 summarizes the myriad efforts used to identify the risk of preterm birth based on bio-markers from asymptomatic women (Vogel et al., 2005).

Serum Biomarkers

Maternal serum is routinely drawn several times during prenatal care. Screening of serum biomarkers for various conditions, such as open neural tube defects and aneuploidy, is already part of routine prenatal care (Canick et al., 2003; Cheschier, 2003). The use of serum biomarkers of spontaneous preterm birth to identify several pathways to preterm birth have been investigated, as described by Romero and colleagues (1994) and Lockwood and Kuczynski (2001) and described in Chapter 6, including (1) activation of maternal or fetal hypothalamic-pituitary-adrenal axis (e.g., corticotropin-releasing hormone) and (2) inflammation due to upper genital tract infection (e.g., defensins and tumor necrosis factor alpha) or decidual hemorrhage or ischemia (e.g., thrombin-antithrombin III complex). No serum biomarkers of pathologic uterine overdistension have been described.

Lower Genital Tract Markers

Bacterial vaginosis (BV) is an alteration of the maternal vaginal flora in which normally predominant lactobacilli are largely replaced by gram-negative anaerobic bacteria, such as Gardnerella vaginalis and Bacteroides, Prevotella, Mobiluncus, and Mycoplasma species. BV in pregnancy is consistently associated with a twofold increased risk of spontaneous preterm birth (Hillier et al., 1995; Meis et al., 1995). The association of BV with preterm birth has been reported to be stronger when the condition is present in the first half of pregnancy (Hay et al., 1994), but a recent analysis of the relationship between gestational age at the time of detection of BV and pregnancy outcome in 12,937 women found "the odds ratio of preterm birth among BV-positive versus -negative women raged from 1.1 to 1.6 and did not vary significantly according to the gestational age at which BV was screened" (Klebanoff et al., 2005, p.). Despite the consistency of the reports relating BV to preterm birth, the clinical utility of tests for BV to identify women at risk is low, owing to the modest strength of the association, the high prevalence of BV in some populations, and the high degrees of variation in the accuracies of the tests used to detect BV (Honest et al., 2004).

Testing of the cervicovaginal secretions of asymptomatic women have been screened for markers of preterm birth, including fetal fibronectin (Goldenberg et al., 1996c 1998), interleukins 6 and 8 (Goepfert et al., 2001; Kurkinen-Raty et al., 2001), and tumor necrosis factor alpha and matrix metalloproteinases (Vogel et al., 2005). The biochemical test for fetal fibronectin is the one about which the most data are available and is the only one marketed in the United States for that purpose.

Fetal Fibronectin

Fetal Fibronectin is a glycoprotein of fetal origin that normally resides at the decidual-chorionic interface within the uterus but is present in cervicovaginal secretions in 3 to 4 percent of pregnant women at between 21 and 37 weeks of gestation (Goldenberg et al., 1996c Lockwood et al., 1991). Evaluation of fibronection levels in asymptomatic women at 24 weeks of gestation has a sensitivity of 20 to 30 percent for the prediction of spontaneous preterm birth at before 35 weeks of gestation (Goldenberg et al., 1996c; Iams et al., 2002). The sensitivity of determination of fibronectin levels for prediction of early preterm births before 28 weeks of gestation was found to be 63 percent (Goldenberg et al., 1996c). Determination of fibronectin levels is a better test for screening for the risk of delivery within 2 weeks of sampling than for delivery before a specific gestational week of pregnancy (Goldenberg et al., 1997).

Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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