[Determination of gestational age by ultrasound]

The authors elaborated a procedure for correction of the gestation age by ultrasonic examination in pregnant women in the second and third trimester of gestation. The method was tested in a group of 500 pregnant women who were examined within the framework of a special ultrasound screening. In 5% of the group the gestation age calculated according to the last menstrual bleeding was not consistent with the results of the ultrasound examination. In these instances a correction was made in case the difference between the ultrasonic finding and the gestation age according to menstruation was two weeks or more, in the first as well as second trimester. In these instances the correction was made with regard to the difference in the first trimester. In the group of women where the correction was made there was in 44% a case-history of irregular menstrual cycles, as compared with 13% in the group where the ultrasonic finding was consistent with the gestation age according to the date of menstruation. In the majority of women (73%) with a shift of the conceiving ovulation the difference of the ultrasonic finding, as compared with the gestation age according to the last menstruation was three weeks or more.