On prediction of the cesarean delivery risk in a large private practice.

OBJECTIVE This study was undertaken to develop an easily usable integrated formula for predicting the probability of cephalopelvic disproportion/failure to progress (CPD) and cesarean delivery (CS) as a function of demographic factors in a middle-class private practice, and to evaluate risk factors for CS in a low-risk primiparous population. METHODS We studied 3355 primiparous women who delivered singleton births between February 1993 and July 2001 in a large private practice. We calculated body mass index (BMI) and weight gain during pregnancy by using clinical data from a comprehensive clinical database. Multivariable logistic regression analysis was used to estimate the relationship between the probability of CS and CS carried out for CPD and 6 demographic factors: maternal age, maternal height, initial pregnancy BMI, pregnancy weight gain, gestational age, and birth weight. Three methods were used to assess the accuracy of the model: the Hosmer-Lemeshow goodness-of-fit statistic, association of predicted probabilities, and direct comparison of the formula to the actual data. Odds ratios with a 95% CI are also calculated for each of these factors. RESULTS The overall rate of primiparous CS for the practice is 21.7%, with 11.7% carried out for CPD. Formulas were developed to predict the probability of CS and the probability of CS caused by CPD. Our analysis shows that both the risk of CS and the risk of CS caused by CPD are significantly associated with all 6 demographic factors. We also develop an easily usable Web page-based calculator to instantly estimate any woman's probability of a CS or CPD at the beginning or at the end of her pregnancy. CONCLUSION The probability of CS and CS performed for CPD is higher for shorter, older, more obese women with large pregnancy weight gains, larger fetal birth weights, and longer gestation ages. Accurate formulas that predict the probabilities of CS and CS performed for CPD in this large private practice have been developed.