Fetal Transverse Cerebellar Diameter / Abdominal Circumference Ratio in Normal Pregnancy

Abstract

Objective To determine the normal values of transverse cerebellar diameter (TCD)/abdominal circumference (AC) ratio during fetal period in Thai population.

Methods Normal singleton pregnancies with certain date between 15 and 40 weeks' gestation were voluntarilly enrolled to undergo ultrasound examination without any specific indications. TCD and AC were measured for each gestational week and the TCD/AC ratio was calculated.

Results TCD/AC ratio was studied in 275 normal pregnancies. By analysis of 944 measurements for each parameter, this ratio was found to be constant and independent of menstrual age, with normal range (mean+2SD) of 13.705+2.016%. The median of the ratio was 13.64% (fifth and 95th percentiles of 11.659 and 15.709, respectively). The mean ratio is nearly the same as that of the western series.

Conclusion The normal TCD/AC ratio is gestational age-independent parameter, constant throughout pregnancy. The ratio obtained from the Thai study hopefully will be the baseline for the Thai population, especially in evaluation of fetal growth in case of uncertain gestataional age.