Prediction of birth weight using the Rossavik growth model: a study in a Dutch population.

OBJECTIVES: To evaluate the Rossavik growth model for predicting birth weight in a Dutch population and to evaluate growth cessation near term. STUDY DESIGN: Birth weight was predicted at various ages between 38 and 42 weeks, menstrual age (MA), and at birth age in 50 normal infants using two sets of ultrasound measurements obtained before 28 weeks, MA. Predicted birth weights were compared to actual weights. The mean percentage difference was used as a measure of systematic error and the standard deviation as a measure of random error. Linear regression analysis was used to evaluate the relationship between percentage differences and birth age. To evaluate the individual growth potential, the Growth Potential Realization Index for weight (GPRIWT) was determined for each fetus. RESULTS: The predictions at 39 and 39.15 weeks, MA, were accurate without systematic error and with a random error of +/-9.3%. Prediction at 38 weeks showed a statistical underestimation (mean +/- SD = -5.8% +/- 8.8), and statistical overestimations were found for predictions after 39.15 weeks and at birth age. A relationship between percentage differences and birth age was not found for predictions between 39.15 and 40 weeks, MA. These findings indicate that growth cessation occurred at 39.15 weeks, MA. Using birth weights predicted at 39.15 weeks, MA, GPRIWT were calculated. The mean GPRIWT value was not significantly different from 100% (p > 0.05), and individual GPRIWT values ranged from 84% to 114%. CONCLUSIONS: The Rossavik growth model can be used to predict birth weight in a Dutch population. However, growth cessation near term appears to occur later than previously reported in other populations.

Predicting head circumference at birth: a study in a Dutch population using the Rossavik growth model.

The use of the Rossavik growth model for predicting neonatal head circumference from data obtained from two ultrasound scans before 28 weeks' menstrual age was investigated in 50 pregnant women with singleton pregnancy in a Dutch population. The head circumference predicted at 38, 39, 39.5 and 40 weeks' gestation and at birth was compared to the head circumference observed at birth. The accuracy was expressed in percentage difference and the growth potential realization index (GPRIHC) was used as an indicator of growth outcome. The predictions at 39.5 weeks and 40 weeks were accurate without systematic error. Prediction at 38 weeks showed a statistical underprediction (mean +/- SD = -2.3 +/- 2.0%, p < 0.05) and at birth a systematic overprediction (mean +/- SD = +1.4 +/- 2.1%, p < 0.05). Based on the regression analyses of percentage differences against birth ages, the growth of the head circumference appeared to stop at about 39.5 weeks. The results of the present study were compared to studies of populations in the United States. The growth of the head circumference before 28 weeks was similar in all samples studied, but growth cessation was at 38 weeks in the fetuses in the USA and at 39.5 weeks in these Dutch fetuses. The mean values of GPRIHC were not different from 100% in all samples studied and the ranges were similar (mean, 100.3%; range, 97-103% in the present study).

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.