The utility of screening for historical risk factors for preterm birth in women with known second trimester cervical length.

OBJECTIVE: To evaluate for the presence of risk factors (RFs) for preterm birth (PTB) in women without prior PTB having second trimester cervical length (CL) screening, and to estimate the utility of RF screening.
METHODS: "Low-risk" singletons were prospectively screened with midtrimester transvaginal ultrasound CL. Prior PTB, intrauterine fetal demise and lethal anomalies were excluded. Women were analyzed based on second trimester CL (<25 mm versus ≥25 mm) and the presence of RFs for PTB. A p-value of < 0.05 was considered significant.
RESULTS: A total of 639 women were screened; 8% had CL <25 mm. Ninety-eight percent of women with CL <25 mm and 95% of women with CL ≥25 mm had RFs for PTB. Five percent of women with a CL ≥25 mm delivered preterm as compared to 18% with CL <25 mm (p < 0.01). Treatment of cervical dysplasia, drug use during the pregnancy and unmarried status were significantly more common in women with CL <25 mm than CL ≥25 mm. When data were analyzed by CL, the presence of additional RFs did not add to the prediction of PTB <37 weeks. DISCUSSION: Over 95% of singleton gestations without prior PTB have ≥1 other RF for PTB. In women without prior PTB, assessment of other PTB RFs does not add to prediction of PTB provided by CL alone.