Longitudinal study of fetal growth in subgroups of a low-risk population.

We investigated fetal weight gain in relation to maternal characteristics within a normal, heterogeneous population in Nottingham, UK. A total of 226 low-risk pregnancies with normal neonatal outcome were examined longitudinally by serial ultrasound examination. Gestation was calculated from early measurements of biparietal diameter. A modified Hadlock's formula for fetal weight was employed, using the biparietal diameter, abdominal circumference and femur length, which was not associated with any significant systematic error. Individual curves were obtained by fitting serial fetal weight estimates and birth weight in a weighted log-polynomial model for fetal growth. The overall growth formula showed an almost linear relationship between gestational age and fetal weight at term. Maternal height and weight at the first hospital visit were positively correlated with fetal weight in the third trimester. The fetuses of parous women were also heavier in late pregnancy, as were those of European compared to Indo-Pakistani mothers. Intrauterine weight gain in the third trimester shows variation with pregnancy characteristics which need to be considered when fetal growth is assessed.