Association between abnormal vaginal flora and cervical length as risk factors for preterm birth.

AIM.: To study the relationship between abnormal vaginal flora (AVF) in the first trimester as a risk factor for shortening cervix length (CL) at second and third trimester, and to assess the combination of these factors in predicting preterm delivery. METHODS.: 1026 unselected low risk women seen before 16 weeks of pregnancy underwent sampling of vaginal fluid for wet mount microscopy at a central laboratory blinded to clinical data. Disappearance of lactobacilli and bacterial vaginosis (BV) were scored according to standardized definitions. Specific cultures were performed for M hominis, U urealyticum, aerobic vaginitis (AV) and vaginal colonization with Candida. CL was measured by transvaginal ultrasound at 10-14, 20-24 and at 30-34 weeks, and gestational age at delivery was recorded. RESULTS.: Short cervix (CL below the lower quartile) at 10-14 weeks is related to a lower CL at 20-24 and 30-34 weeks of gestation (p=0.01, p=0.005 respectively). Short cervix at 20-24 weeks, but not at 10-14 weeks, was predictive for preterm birth. In patients with M. hominis and/or with severe AV at 10-14 weeks, the cervix appeared shorter at 20-24 and at 30-34 weeks than in other women. Increased risk for preterm birth in women with a shorter cervix at 10-14 weeks and AVF could not be proved by this study. DISCUSSION.: Presence of AV or M. hominis is associated with a shorter cervix at 20-24 and 30-34 weeks. Although a short cervix at 10-14 weeks increases the likelihood of having a short cervix later in pregnancy, it was not a prerequisite for AVF to be associated with preterm delivery. Therefore, in the pathogenesis of preterm birth, certain types of AVF may be involved directly in the process of cervical shortening, rather than being exposed to the intrauterine cavity more readily by a short cervix in the early stages of pregnancy. Copyright (c) 2010 ISUOG. Published by John Wiley & Sons, Ltd.