Comparative Accuracy of Trans Cerebellar Diameter and Crown Rump Length for Estimation of Gestational Age

Many Indian women present for the first antenatal check up in third trimester and most of them have unreliable LMP with no early scans. To compare the predicted accuracy of third trimester transcerebellar diameter and first trimester crown rump length for estimation of gestational age. A cross sectional study was conducted on 198 eligible antenatal women in 3rd trimester, having early scans showing CRL. Transcerebellar diameter (TCD) was measured and compared with 1st trimester CRL for accurately estimating the gestational age based on LMP. It was found that there is linear rise in TCD along with gestational age and TCD in mm corresponded to the gestational age in weeks. TCD was accurate in 90.6% women between 29 to 31 weeks and then accuracy was increased reaching 94.7% (33+1 to 35 wks) and 93.8% (37+ to 40 wks). The efficacy of 3rd trimester TCD is comparable to 1st trimester CRL for estimation of gestational age.