Estimation of gestational age using crown-rump length (CRL) has been considered to be relatively accurate. Thepurpose of this study was to determine the relationship between the gestational age (GA) and the CRL seen ontransvaginal sonography and to improve the gestational dating creteria. One hundred and ninty five patients withknown date of conception, who were pregnant between February 1990 and December 1992, were examined with highresolution transvaginal ultrasonography. There was a linear relationship between the CRL and the GA from the 27thto the 56th day of ovulation. It was defined by equation, as GA=0.97xCRL+42.4 (r=0.95, p<0.0001). Regressionvalues with 95% confidence limit for CRL were +3.9-4.0days. Comparison of regression lines between the data fromthe natural cycle group (N=53) and those from the hormonally treated group (N=142) was performed. There was nostatistically significant difference between the two groups (analysis of convariance, p>0.05) In conclusion,trasvaginal sonography was useful in the detrermination of the GA in the early pregnancy from the 27th daly ofovulation up to the 56th day. A new reference chart is provided for the estimation of gestational age according tothe CRL.
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