Association patterns of fetal head dimensions, postcranial body growth and neonatal size.

The association patterns between fetal biometry at the first, second and third trimester and neonatal size were analyzed using a dataset of 3814 singleton term birth taking place at the Viennese Danube hospital in Austria between 2005 and 2013. In this electronic medical record-based study, fetal biometry was estimated by the results of three ultrasound examinations carried out at the 11/12, 20/21 and 32/33week of gestation. In detail, crown-rump length, biparietal diameter, fronto-occipital diameter, head circumference, abdominal transverse diameter, abdominal anterior-posterior diameter, abdominal circumference, and femur length were determined. Birth weight, birth length and head circumference were measured within one hour after birth. Fetal head size, abdominal dimensions and femur length intercorrelated positively from the second trimester onwards and correlated significantly positively with neonatal size (r = 0.04 to 0.46). Despite these allometric associations between fetal and newborn parameters, principal component analyses showed that parameters indicating body fat/weight, head or brain size and skeletal growth load on separate components. Consequently, under optimal circumstances during pregnancy, head growth, fat accumulation and skeletal growth show independent incremental patterns from the second trimester onwards.