Prediction of the neonatal crown-heel length from femur diaphysis length measurements.

The usefulness of the Rossavik growth model in predicting crown-heel length (CHL) was evaluated in 50 women with normal singleton pregnancies in a Dutch population. The femur diaphysis lengths (FDL) were predicted assuming growth cessation at 38, 39, 39.5, and 40 weeks, menstrual age (MA), and at birth using Rossavik growth models determined from two second-trimester FDL measurements. Predicted CHLs were then calculated from predicted FDLs using six different equations. Predicted CHLs were compared with the actual neonatal CHLs and the percent differences calculated. The growth potential realization index (GPRI) values were also determined. With all six equations, regression analysis revealed a significant relationship between the percent differences and birth ages for those infants delivering after 38 and 39 weeks, MA, respectively. The signs of the slopes of the regression lines were negative, indicating continued growth of these fetuses. With the Vintzileos equation, 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 GPRICHL was 99%, with a 95% range of 93% to 104%. These findings indicate that the CHL can be predicted with a high degree of accuracy in this Dutch population if the appropriate growth cessation age and FDL-CHL function are used.