Prediction of delivery among women with early preterm labor by means of clinical characteristics alone.

OBJECTIVE This study was undertaken to assess whether individual clinical factors or combinations thereof could be used to accurately predict the risk of delivery within 1 week of admission among women with preterm labor and minimal cervical dilatation. STUDY DESIGN We performed a case-control study of patients admitted to our institution with preterm labor and minimal cervical dilatation. A case patient was a patient who sought treatment with uterine contractions between 24 and 34 weeks' gestation with cervical dilatation </=2 cm, who received tocolysis with magnesium sulfate, and who was delivered within 7 days of admission. Control subjects were those who had the same presentation with preterm labor but were not delivered within the first 7 days after admission. The medical records of case patients and control subjects were then abstracted, and information on >70 potential predictors was recorded. Statistical analysis consisted of bivariate and multivariable methods. We also generated a multivariable clinical predictive model with the purpose of detecting a proportion as high as possible of those destined to be delivered within 1 week (high sensitivity). We estimated that we would need 50 case patients and 150 control subjects to detect an odds ratio of 2.5 for risk factors with a prevalence of 20%, an alpha error of.05, a beta error of.20, and a control subject/case patient ratio of 3:1. RESULTS Three variables were eligible for inclusion in our logistic models according to the bivariate analyses-bleeding on admission, substance abuse, and admission white blood cell count >/=14,000 cells/microL. The simplest and most favorable model included only 2 variables, bleeding and substance abuse, and yielded a sensitivity of 46% and a specificity of 76%. The full 3-variable model had similar test characteristics. For no model were we able to achieve a sensitivity >/=50%. CONCLUSION The results of this case-control study suggest that combinations of clinical factors do not yield an adequate level of discrimination to be used alone for predicting the likelihood of delivery within 1 week among patients with minimal degrees of cervical dilatation.