Anthropometric measurements in the second trimester fetus

Normal anthropometric measurements, of accepted value for clinicians and pathologists in the assessment of the dysmorphic neonate, have not in the past been available for the second trimester fetus, in which dysmorphic features are often more subtle and objective measurements most needed. In order to establish these values 19 anthropometric measurements, comparable to those published for the larger fetus and neonate, were recorded at autopsy on each of 260 overtly normal non-macerated singleton fetuses between 13 and 26 weeks gestation. Regression lines for each parameter, and growth ratios of potential value for description and assessment of dysmorphic features, were derived. The sex ratio was 1.27 and as there was no statistically significant sex difference for any of the 19 measurements chosen, the data was subsequently pooled. There were linear correlations between gestational age and each growth parameter, all but three exceeding 0.90. The linear correlations between pairs of growth parameter were higher than the correlations between gestational age and individual growth parameters. This suggests that growth parameter pairs, expressed as a ratio, are less affected by errors in gestational age estimation. Ratios enabling the dysmorphologist to more objectively assess common observations such as abnormalities of head shape, relationship between limb and trunk length and gross proportional relationships between major body segments were derived. Collected measurements were compared with established ultrasound reference ranges. While reference ranges for biparietal diameter and head circumference showed close concordance with those derived from ultrasound measurements, the abdominal circumference was consistently lower than that measured by ultrasound possibly because of differing trunk positions in utero compared with after death. The graphs and ratios derived in this study can be rapidly applied to confirm visual impressions at clinical examination and at autopsy.