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The Preterm Prediction Study: toward a multiple-marker test for spontaneous preterm birth.

OBJECTIVE
The Preterm Prediction Study evaluated 28 potential biologic markers for spontaneous preterm birth in asymptomatic women at 23 to 24 weeks gestational age. This analysis compares those markers individually and in combination for an association with spontaneous preterm birth at <32 and <35 weeks gestational age.


STUDY DESIGN
With the use of a nested case-control design from an original cohort study of 2929 women, results of tests from 50 women with a spontaneous preterm birth at <32 weeks and 127 women with a spontaneous preterm birth at <35 weeks were compared with results from matched-term control subjects.


RESULTS
In the univariate analysis, the most potent markers that are associated with spontaneous preterm birth at <32 weeks by odds ratio were a positive cervical-vaginal fetal fibronectin test (odds ratio, 32.7) and <10th percentile cervical length (odds ratio, 5.8), and in serum, >90th percentiles of alpha-fetoprotein (odds ratio, 8.3) and alkaline phosphatase (odds ratio, 6.8), and >75th percentile of granulocyte colony-stimulating factor (odds ratio, 5.5). Results for spontaneous preterm birth at <35 weeks were generally similar but not as strong. Univariate and multivariate logistic regression analyses demonstrated little interaction among the tests in their association with spontaneous preterm birth. Combinations of the 5 markers were evaluated for their association with <32 weeks spontaneous preterm birth. Ninety-three percent of case patients had at least 1 positive test result versus 34% of control subjects (odds ratio, 24.0; 95% CI, 6.4-93.4). Among the case patients, 59% had >or=2 positive test results versus 2.4% of control subjects (odds ratio, 56.5; 95% CI, 7.1-451.7). If a cutoff of 3 positive test results was used, 20% of case patients and none of the control subjects had positive test results (P < .002). With the use of only the 3 serum tests (alkaline phosphatase, alpha-fetoprotein, and granulocyte colony-stimulating factor), any positive test identified 81% of cases versus 22% of control subjects (odds ratio, 14.7; 95% CI, 5.0-42.7). For spontaneous preterm birth at <35 weeks gestation, any 2 positive tests identified 43% of cases and 6% of control subjects (odds ratio, 11.2; 95% CI, 4.8-26.2).


CONCLUSION
Overlap among the strongest biologic markers for spontaneous preterm birth is small. This suggests that the use of tests such as maternal serum alpha-fetoprotein, alkaline phosphatase, and granulocyte colony-stimulating factor as a group or adding their results to fetal fibronectin test and cervical length test results may enhance our ability to predict spontaneous preterm birth and that the development of a multiple-marker test for spontaneous preterm birth is feasible.