[The weekly growth variations of the principal fetal echographic biometric parameters in pregnancy]. 
The aim of this study was to describe the normal range for the measurement of sonographic fetal parameters in our population, analyzed growth trend in different periods of pregnancy and establish the optimal time interval between scans.  The study was performed in 2336 normal pregnant women between 14-40 weeks of gestation.  Polynomial regression analysis was used to describe growth curves.  A persistent increment of all ultrasonographic parameters throughout pregnancy was observed with a very high correlation with gestational age.  A flattening of growth curves was observed after the 30th week of gestation for cephalic parameters and after the 28th week for the other parameters, particularly for fetal limb measurements.  Considering inter- and intra-operator error and the physiological weekly increment, a correct growth evaluation of single parameters requires at last a two weeks time span from the last scan performed.  Only the biparietal diameter and femur length allow a correct growth evaluation weekly, before the 30th week and the 28th week, respectively.