[Estimation of gestational age by ultrasonic measurements of the gestational sac].

One hundred and eighty gestational sac (GS) measurements by ultrasound echography were performed on 132 healthy pregnant women with an accurate gestational age of between five and twelve weeks. Their prenatal courses were uneventful and they delivered of babies appropriate for dates at term. The GS longest diameter in longitudinal section (LGS), the GS longest diameter making perpendicularity to LGS in the same section (VGS) and the GS longest horizontal diameter in transversal section (TGS) were measured in cm. GS maximum diameter, two directional GS diameters (LGS¥TGS, LGS¥VGS, TGS¥VGS) and three directional GS diameters (LGS ¥ TGS ¥ VGS) were assessed by computer analysis for correlation with gestational age and for comparison. 1) Good correlation was obtained between GS maximum diameter and gestational age, with a correlation coefficient of 0.926105 and a standard error of 0.624265. 2) The geometric or arithmetric means of LGS and TGS correlated most with gestational age in two directional GS diameters. The aritbmetric means of LGS and TGS correlated with gestational age better than the geometric means, with a correlation coefficient of 0.936251 and a standard error of 0.594649. 3) The arithmetric means of three directional GS diameters correlated with gestational age better than the geometric means, with a correlation coefficient of 0.947145 and a standard error of 0.542982. 4) The above results indicated that the measurements of the arithmetric means of three directional GS diameters exceedingly reduces errors in estimating gestational age. 5) A convertible table to estimate gestational age on GS maximum diameters, arithmetric means of LGS and TGS, and of three directional GS diameters was made.