Predicting delivery within 48 hours in women treated with parenteral tocolysis

Objective: To develop a prediction rule using clinical admission characteri stics for women treated with parenteral tocolysis for preterm labor who are at highest risk of delivery within 48 hours. Methods: We performed a case-control study of patients treated with magnesi um sulfate for idiopathic preterm labor. A case was defined as a patient wh o received magnesium sulfate tocolysis and delivered within 48 hours of adm ission. We selected a 48-hour delay to delivery as a clinically relevant en dpoint for the maximization of steroid benefit. Controls were patients who received magnesium sulfate tocolysis and remained undelivered 48 hours afte r admission. Cases and controls were identified by merging a pharmacy billi ng database with International Classification of Disease codes for prematur e labor. Medical records were reviewed and risk factor information was obta ined. We focused on risk factors within the first hour of admission, becaus e our goal was to identify patients at high risk of delivery early in their hospital course. Backward stepwise logistic regression was used to develop explanatory and predictive models. The focus of the predictive model was t o maximize the test's sensitivity and negative predictive value. Results: We identified 50 cases and 150 controls. The following six variabl es were included in the initial multivariable models based on bivariate ana lyses: white blood cell count at least 14.0 (1000/mu L), cervical dilation at least 2 cm, bleeding, substance abuse, parity, and previous abortion. A two-variable model containing cervical dilation and bleeding had an overall accuracy of 73%, sensitivity of 62%, and specificity of 76%, and it was as sensitive and specific as more complex models. Conclusions: Cervical dilation of at least 2 cm and bleeding on admission h ad an overall accuracy of 73% in predicting the likelihood of delivery with in 48 hours in women receiving magnesium sulfate. (C) 1999 by The American College of Obstetricians and Gynecologists.