As discussed on page 810, a link between some cases of preterm birth and infection seems irrefutable (Goldenberg, 2008). In several studies, antimicrobial treatment has been given to prevent preterm labor thought to be due to microbial invasion. These strategies especially targeted Mycoplasma species. Morency and colleagues (2007) performed a metaanalysis of 61 articles and suggested that antimicrobials given in the second trimester may prevent subsequent preterm birth. Andrews and associates (2006) reported results of a randomized trial in which they gave a course of azithromycin plus metronidazole every 4 months to 241 nonpregnant women whose last pregnancy resulted in spontaneous delivery before 34 weeks. Approximately 80 percent of the women with subsequent pregnancies had received study drug within 6 months of their subsequent conception. Such interconceptional antimicrobial treatment did not reduce the rate of recurrent preterm birth. Using a subgroup analysis of these same women, Tita and coworkers (2007) concluded that such use of antimicrobials may be harmful. In another randomized study, 2661 women received placebo or metronidazole plus erythromycin between 20 and 24 weeks' gestation followed by ampicillin plus metronidazole during labor (Goldenberg, 2006). his antimicrobial regimen did not reduce the rate of preterm birth or that of histological chorioamnionitis. At this time, antibiotic prophylaxis to prevent preterm birth is not recommended in women with preterm labor and intact membranes (Flenady,r2013).
In this condition, normal, hydrogen peroxide-producing, lactobacillus-predominant vaginal flora is replaced with anaerobes (Hillier, 1995; Nugent, 1991). Its diagnosis and management are discussed in Chapter 65 (p. 1245). Using Gram staining, relative concentrations of the bacterial morphotypes characteristic of bacterial vaginosis are determined and graded by the Nugent score or assessed clinically with Amsel criteria.
Bacterial vaginosis has been associated with spontaneous abortion, preterm labor, PPROM, chorioamnionitis, and amnionic fluid infection (Hillier, 1995; Kurki, 1992; Leitich, 2003a,b). Environmental factors appear to be important in bacterial vaginosis development. Exposure to chronic stress, ethnic diferences, and frequent or recent douching are associated with higher rates of the condition (Culhane, 2002; Ness, 2002). A gene-environment interaction has also been described (Macones, 2004). Women with bacterial vaginosis and a susceptible TNF-a genotype had a ninefold increased incidence of preterm birth.
From all of these studies, adverse vaginal flora seems associated with spontaneous preterm birth. Unfortunately, to date, screening and treatment have not prevented preterm birth. These are discussed further in Chapter 65 (p. 1246). Indeed, microbial resistance or antimicrobial-induced change in the vaginal flora results from regimens intended to eliminate bacterial vaginosis (Beigi, 2004; Carey, 2005).
Early diferentiation between true and false labor is diicultespecially before demonstrable cervical efacement and dilation. Uterine activity alone can be misleading because of Braxton Hicks contractions. These irregular, nonrhythmical contractions can cause considerable confusion in the diagnosis of true labor. Not infrequently, women who deliver before term have uterine activity that is attributed to Braxton Hicks contractions that prompt an incorrect diagnosis of false labor. Accordingly, the American College of Obstetricians and Gynecologists (2016b) defines preterm labor to be regular contractions before 37 weeks that are associated with cervical change.