The Preterm Prediction Study: Sequential cervical length and fetal fibronectin testing for the prediction of spontaneous preterm birth

Objectives: This study was undertaken to further elucidate the pathogenesis of preterm birth by means of traditional risk factors and new markers for preterm birth derived from the Preterm Prediction Study. Study Design: A total of 3076 women (2929 with singleton gestations and 147 with twin pregnancies) were categorized according to the presence of risk factors including black race, low body mass index, the presence of bacterial vaginosis, and previous preterm birth. At 24 and 28 weeksʹ gestation cervical length was measured and categorized as short (< 25 mm) or normal (>25 mm). Vaginal and cervical fetal fibronectin concentrations were measured at 24, 26, 28, and 30 weeksʹ gestation and results were categorized as positive (≥50 ng/mL) or negative (<50 ng/mL) Results: At 24 to 26 weeksʹ gestation women with each of the risk factors were more likely to have positive fibronectin test results or to have a short cervix. Among women with negative fetal fibronectin results at 24 to 26 weeksʹ gestation those with a short cervix were more likely to have positive fetal fibronectin results at 28 to 30 weeksʹ gestation, and among those with normal cervical length those women who had positive fetal fibronectin results were more likely to have a short cervix at later evaluation. Most women who had positive fetal fibronec in results at 24 to 26 weeksʹ gestation had negative results at 28 to 30 weeksʹ gestation, whereas most but not all women who had a short cervix at 24 to 26 weeksʹ gestation still had a short cervix at 28 to 30 weeksʹ gestation. In each period women with both a positive fetal fibronectin result and a short cervix were at substantially increased risk of spontaneous preterm birth; women with either marker alone had intermediate and approximately equal risks of spontaneous preterm birth, and women without either marker had a low risk of spontaneous preterm birth Conclusions: Regardless of other risk factors, a short cervix predicts a subsequent positive fetal fibronectin result, and a positive fetal fibronectin result predicts subsequent cervical shortening. These data do not support a single sequence of events leading to spontaneous preterm birth.