Fetal pelvic index to predict cephalopelvic disproportion - a retrospective clinical cohort study.

OBJECTIVE: To investigate the diagnostic accuracy of the fetal pelvic index to predict cephalopelvic disproportion.

DESIGN: Retrospective observational cohort study.

SETTING: Pregnant women who had been examined by X-ray or magnetic resonance imaging pelvimetry because of an increased risk of fetal-pelvic disproportion during 2000-2008 in North Karelia Central Hospital.

POPULATION: A total of 274 pregnant women.

METHODS: Univariable and multivariable regression analyses were carried out to identify risk factors for cesarean section. Diagnostic accuracy was tested with a receiver operating characteristic curve, and the optimal cut-off value for fetal pelvic index was calculated.

MAIN OUTCOME MEASURE: Cesarean section rates.

RESULTS: A total of 242 women delivered vaginally, and 32 delivered with cesarean section caused by labor arrest. In multivariable modeling, the fetal pelvic index, maternal pelvic inlet size, fetal head circumference and maternal age were significantly associated with a risk of cesarean section. In the receiver operating characteristic analysis, the area under curve was 0.686 with a p-value of 0.001 and a 95% confidence interval of 0.595-0.778. The optimal fetal pelvic index cut-off value according to the receiver operating characteristic was -0.65. The cesarean section rate was 8% below the fetal pelvic index value of -0.65 and 20% above the fetal pelvic index value of -0.65.

CONCLUSIONS: The fetal pelvic index was not a clinically useful tool to predict the mode of delivery for patients at high risk of cephalopelvic disproportion. The pooled analysis of the current and previous studies strengthened this conclusion.