Transvaginal Sonographic Measurements of Crown Rump Length as a Predictor of Gestational Age

Abstract

The relation between fetal crown-rump length (CRL) and gestational age was determined by crossed sectional analysis of 251 normal fetuses (6-14 weeks) using transvaginal sonography. Mathematical modelling of the data demonstrated that the CRL growth curve is nonlinear. Predicted menstrual age values in days for specific CRL measurements in millimeters were calculated and are reported in tabular forms. The variability (+ 2 SD) associated with predicting menstrual age from CRL is + 5.8 days between 6-14 weeks. CRL can be used as an adjunct in estimating menstrual age, and may be useful in predicting fetal outcome of threat ened abortion in the first trimester. Predicted CRL values at various points in gestation were comparable to the results of other investigators. (Thai J Obstet Gynaecol 1993;5:1-5.)