New quantitative patterns of the growing trachea in human fetuses

Rapid progress in perinatal medicine has resulted in numerous tracheo-bronchial interventions on fetal and neonatal airways. The present study was performed to compile normative data for tracheal dimensions at varying gestational ages.

Using anatomical dissection, digital image analysis (NIS-Elements BR 3.0) and statistical analysis (Wilcoxon signed-rank test, Student's t test, one-way ANOVA, post-hoc Bonferroni test, linear and nonlinear regression analysis) a range of the 4 variables (length in mm, middle external transverse diameter in mm, proximal internal cross-sectional area in mm², internal volume in mm³) for the trachea in 73 spontaneously aborted human fetuses (39 male, 34 female) aged 14-25 weeks was examined.

No significant male-female differences were found (P>0.05). The length ranged from 10.37±2.15 to 26.54±0.26 mm as y=-65.098 + 28.796 × ln (Age) ±1.794 (R²=0.82). The middle external transverse diameter varied from 2.53±0.09 to 5.09±0.42 mm with the model y=-11.020 + 5.049 × ln (Age) ±0.330 (R²=0.81). The trachea indicated a proportional evolution because the middle external transverse diameter-to-length ratio was stable (0.23±0.03). The proximal internal cross-sectional area rose from 1.46±0.04 to 5.76±1.04 mm² as y=-3.562 + 0.352 × Age ±0.519 (R²=0.76). The internal volumetric growth from 11.89±2.49 to 119.63±4.95 mm³ generated the function y=-135.248 + 9.919 × Age ±10.478 (R²=0.86).

The growth in both length and middle external transverse diameter of the trachea follows logarithmic functions, whereas growth of both its proximal internal cross-sectional area and internal volume follow linear functions. The length and middle external transverse diameter of the trachea develop proportionally to each other. The tracheal dimensions may be helpful in the prenatal diagnosis and monitoring of tracheal malformations and obstructive anomalies of the upper respiratory tract.