Symphysis-fundus measurement - the predictive value of a new reference curve.

BACKGROUND: Symphysis-fundus measurement is used in pregnancy care to detect poor fetal growth. Symphysis-fundus measurement curves (percentile curves) and prediction of fetuses with a birth weight below the10th percentile have been published previously. The percentile curves show the distribution of symphysis-fundus measurements in the reference population and are recommended as the national standard. This article discusses the predictive value of this method for identification of neonates who are small for gestational age (SGA).

MATERIAL AND METHOD: This is a population-based registry study of pregnant women who gave birth at Sahlgrenska University Hospital in Gothenburg in the period 2005 – 2010. Diagnostic accuracy was analysed using ROC curves and presented with the area under the curve (AUC) from gestational week 24 to 42. Sensitivity, specificity, and positive and negative predictive value were calculated.

RESULTS: A total of 42 018 pregnant women carrying a single fetus were included. The AUC values showed that a symphysis-fundus measurement late in pregnancy was a stronger predictor for determining fetuses that are small for gestational age than a measurement early in pregnancy. The AUC value increased from 0.61 in week 24 to 0.74 in week 40. With a threshold value at the 10th percentile, symphysis-fundus measurement has a total sensitivity of 47 % and a specificity of 79 %. A positive total test was defined as at least one measurement below the 10th percentile curve in the course of the pregnancy.

INTERPRETATION: Symphysis-fundus measurement may be important for the identification of high-risk pregnancies, but should preferably be used in conjunction with other clinical variables.