PREDICTION OF THE NEONATAL CROWN-HEEL LENGTH FROM FEMUR DIAPHYSIS LENGTH MEASUREMENTS

The usefulness of the Rossavik growth model in predicting crown-heel l ength (CHL) was evaluated in 50 women with normal singleton pregnancie s in a Dutch population. The femur diaphysis lengths (FDL) were predic ted assuming growth cessation at 38, 39, 39.5, and 40 weeks, menstrual age (MA), and at birth using Rossavik growth models determined from t wo second-trimester FDL measurements. Predicted CHLs were then calcula ted from predicted FDLs using six different equations. Predicted CHLs were compared with the actual neonatal CHLs and the percent difference s calculated. The growth potential realization index (GPRI) values wer e also determined. With all six equations, regression analysis reveale d a significant relationship between the percent differences and birth ages for those infants delivering after 38 and 39 weeks, MA, respecti vely. The signs of the slopes of the regression lines were negative, i ndicating continued growth of these fetuses. With the Vintzileos equat ion, no evidence of continued growth was obtained after 39.5 weeks, MA . The systematic prediction error at this time point was 0.9%, whereas the random error was 3.3%. The mean GPRI(CHL) was 99%, with a 95% ran ge of 93% to 104%. These findings indicate that the CHL can be predict ed with a high degree of accuracy in this Dutch population if the appr opriate growth cessation age and FDL-CHL function are used. (C) 1994 J ohn Wiley and Sons, Inc.