Sonographic Determination of Gestational Age in the Second and Third Trimester from Transverse Cerebellar Diameter Among Pregnant Women in Enugu, Nigeria

ABSTRACT Fetal transverse cerebellar diameter (TCD) was found to be useful in gestational age (GA) assessment during routine fetal ultrasound examination. The aim of this study is to establish normogram of fetal TCD in the second and third trimesters of pregnancy and to compare its ability to predict gestational age with previously published nomograms. Six hundred and ninety seven pregnant women with GA between 14 and 40 weeks were scanned using convenience sampling method. Each woman had three ultrasonographic measurements and the best average was obtained. Transverse cerebellar diameter was measured from transverse view of fetal intracranial anatomy through the posterior fossa that included visualization of anatomic landmarks such as thalamus, cavum septum pellucidium and cisterna magna. The TCD measurement was obtained by placing electronic calipers from proximal outer margin to distal outer margin of cerebellum. The women’s last menstrual period (LMP) and fetal femur length (FL), biparietal diameter (BPD), head circumference (HC), and abdominal circumference (AC) of the fetuses were also recorded. Values of transverse cerebellar diameter obtained were used to determine fetal gestational age. The mean TCD increases from 13.6 ± 2.2 mm to 27.3 ± 2.6 mm in the second trimester and 28.9 ± 2.0 mm to 42.9 ± 2.0 mm in the third trimester. The relationship of TCD with GA obtained from LMP and FL, BPD, HC and AC were determined. The TCD has a strong correlation with GA (r = 0.93; p < 0.05). Model equations: GA = 0.63 (TCD) + 7.16 I; GA = 0.54 (TCD) + 14.32 and GA = 0.79 (TCD) + 4.91 in the second, third and combined trimesters were generated. There is no statistically significant difference found between the mean TCD values obtained in this study from that of the previous literatures (p>0.05). The normogram of transverse cerebellar diameter generated shows that TCD can be a good estimator of fetal GA from 14 weeks to term.