title: The diagnostic accuracy of pelvic measurements: threshold values and fetal size.
abstract: OBJECTIVE
  This study aimed to correlate pelvic dimensions and fetal size to the risk for cesarean section caused by protracted labor.
  
  
  METHODS
  This is an observational, retrospective cohort study on pregnant women with an increased risk of labor dystocia. After pelvimetry, pelvic adequacy was clinically tested in a trial of labor. A multivariable regression analysis was made to identify the risk factors for cesarean section. Two subgroups were established according to the size of the estimated fetal head circumference (HC) (arbitrary cutoffs of ≤340 and >340 mm), and the pelvic measurements were compared by the mode of delivery. Receiver operating characteristic (ROC) curves were evaluated.
  
  
  RESULTS
  Altogether, 274 patients were ultimately included. The mean size of the maternal inlet was 1.0 cm larger in fetal HC >340 mm group compared with ≤340 mm. In the vaginal delivery group, the difference was 1.3 cm. In the multivariable modeling, maternal age (odds ratio [OR] 1.09, 95 % confidence interval [CI] 1.02-1.17), fetal HC (OR 1.05, 95 % CI 1.02-1.09), and maternal inlet circumference (OR 0.95, 95 % CI 0.92-0.97) had significance for the risk of cesarean section. In the ROC analysis, the area under the curve (AUC) value for the pelvic inlet was 0.736 (p < 0.001, 95 % CI 0.656-0.816), and in the subgroups with fetal HC ≤340 and >340 mm, AUCs were 0.634 (p < 0.11, 95 % CI 0.493-0.775) and 0.836 (p < 0.001, 95 % CI 0.751-0921), respectively.
  
  
  CONCLUSIONS
  Labor arrest was associated with the linear relationship between the maternal pelvic dimensions and the fetal size. Therefore, the approach should be changed from standardized pelvimetric threshold values to passenger-passageway ratio analyzed by multivariable modeling to find more accurate methods to predict cephalopelvic disproportion.
authors.affiliation: Department of Obstetrics and Gynecology, Kuopio University Hospital, Kuopio, Finland, ulla.korhonen@pkssk.fi.
authors.forename: U
authors.initials: U
authors.lastname: Korhonen
authors.forename: P
authors.initials: P
authors.lastname: Taipale
authors.forename: S
authors.initials: S
authors.lastname: Heinonen
mesh_terms: D000328:Adult; D002508:Cephalometry; D052178:Cephalopelvic Disproportion / Q000175:diagnosis; D002585:Cesarean Section / Q000706:statistics & numerical data*; D015331:Cohort Studies; D005260:Female; D006257:Head / Q000000981:diagnostic imaging* / Q000196:embryology; D006801:Humans; D007751:Labor, Induced / Q000706:statistics & numerical data; D008423:Maternal Age; D015999:Multivariate Analysis; D010120:Oxytocics / Q000627:therapeutic use; D010121:Oxytocin / Q000627:therapeutic use; D010387:Pelvimetry; D011247:Pregnancy; D012372:ROC Curve; D012189:Retrospective Studies; D012307:Risk Factors; D014219:Trial of Labor; D016216:Ultrasonography, Prenatal; D055815:Young Adult
chemical_list: D010120:Oxytocics; D010121:Oxytocin