Transvaginal cervical length and tobacco use in Appalachian women: association with increased risk for spontaneous preterm birth.

Currently ACOG recommends that a mid-term screening strategy may be considered to identify short cervix in low risk populations in an effort to prevent preterm birth. Vaginal progesterone is recommended for women with a cervical length ≤20 mm. Cerclage is recommended for women with prior spontaneous preterm birth who are already receiving progesterone supplementition and CL is <25 mm. This study examined risk factors for spontaneous preterm birth (SPB) <35 weeks among a general obstetrical population prior to these ACOG recommendations. However, cervical cerclage was a possible intervention. Study population included 1,074 patients from 1 Jan 2007-30 Jun 2008 receiving mid-trimester transvaginal ultrasounds during prenatal care at a tertiary medical center clinic. Receiver operator characteristic (ROC) curve cutoff optimal value was ≤34 mm, (n=224), corresponding to 8.9% SPB with shortened cervices compared to 1.4% in patients with normal cervices (>34 mm; n=850; p<0.001 (Area Under the Curve (AUC) 76.6, p<0.001). Cervical lengths <30 mm had 12 times the risk of SPB (p<0.001) while 30-34 mm had 5 times (p=0.005). Tobacco use (≥10 cigarettes per day), p=0.030, and low BMI, p=0.034, had additive effect. Shortened cervical length during routine screening independently predicted SPB while heavy smoking with shortened cervix during pregnancy doubled risk compared to shortened cervix alone.