Reference Charts for Fetal Cerebellar Vermis Height: A Prospective Cross-Sectional Study of 10605 Fetuses

Abstract

Objective: To establish reference charts for fetal cerebellar vermis height in an unselected population.

Methods: A prospective cross-sectional study between September 2009 and December 2014 was carried out at ALTAMEDICA Fetal-Maternal Medical Centre, Rome, Italy. Of 25203 fetal biometric measurements, 12167 (48%) measurements of the cerebellar vermis were available. After excluding 1562 (12.8%) measurements, a total of 10605 (87.2%) fetuses were considered and analyzed once only. Parametric and nonparametric quantile regression models were used for the statistical analysis. In order to evaluate the robustness of the proposed reference charts regarding various distributional assumptions on the ultrasound measurements at hand, we compared the gestational age-specific reference curves we produced through the statistical methods used. Normal mean height based on parametric and nonparametric methods were defined for each week of gestation and the regression equation expressing the height of the cerebellar vermis as a function of gestational age was calculated. Finally the correlation between dimension/gestation was measured.

Results: The mean height of the cerebellar vermis was 12.7mm (SD, 1.6mm; 95% confidence interval, 12.7-12.8mm). The regression equation expressing the height of the CV as a function of the gestational age was: height (mm) = -4.85+0.78 x gestational age. The correlation between dimension/gestation was expressed by the coefficient r = 0.87.

Conclusion: This is the first prospective cross-sectional study on fetal cerebellar vermis biometry with such a large sample size reported in literature. It is a detailed statistical survey and contains new centile-based reference charts for fetal height of cerebellar vermis measurements.

Fig 1. Measurement of the cerebellar vermis height.

Fig 2. Anderson-Darling tests and the associated diagnostic plots.

Top left, Box plot of the original measurements. Bottom left, Raw p-values associated with the Anderson-Darling test of normality for the original measurements. Top right, Box plot of the log-transformed data. Bottom right, Raw p-values associated with the Anderson-Darling test of normality for the log-transformed data. The sizes of the circles in the bubble plot are proportional to the numbers of samples (n) available during that week.

Fig 3. Normal-based mean curve.

95^th and 5^th centile curves across gestational age.

Fig 4. Z score.

Diagnostic plots for the original measurements.

Fig 5. Z score.

Diagnostic plots for the log-transformed data.

Fig 6. GAMLSS diagnostic plots.

Fig 7. Shape-constrained quantile regression (QR).

Estimates for the conditional median and approximate confidence bands (point-wise bands in dark gray, uniform bands in light gray) compared with the standard normal-based fit.

Fig 8. Shape-constrained quantile regression (QR).

Estimates for a range of levels of interest and approximate confidence bands (point-wise bands in dark gray, uniform bands in light gray) compared with the standard normal-based fit.