Maternal blood levels of human placental lactogen in the prediction of fetal growth retardation: choosing a cut‐off point between normal and abnormal

Single estimations of serum human placental lactogen (hPL) were made in 527 unselected women between 36 and 40 weeks gestation. The association between decreased serum levels of hPL and intrauterine growth retardation was confirmed. The effect of changing the cut-off point between normality and abnormality on the sensitivity, specificity and predictive value was determined. When the 10th centile of hPL values was used, 29% of all growth-retarded fetuses were identified and 91% of all 'normal' fetuses were excluded. The 15th and 25th centiles yielded improved sensitivities of 37 and 50% respectively, but specificity was reduced. It is suggested that the 10th centile provides a good compromise between sensitivity on the one hand and specificity and predictive value on the other.