[Ultrasonic biometry of the fetal crown-rump length between 7 and 20 weeks gestation (author's transl)].

In 370 examinations on 258 patients with known gestational age crown-rump length (CRL) of the fetus was determined by sonar between 7 and 20 weeks. From the results the mean and "2 SD" limits of CRL were derived by means of a non linear regression analysis. The measurements were further analysed to determine gestational age for a given CRL. Besides a velocity curve of CRL growth was calculated. It showed a maximum of 1.8 mm per day at 14 weeks. It was confirmated that sonar measurements of crown-rump length are very useful to estimate maturity of the fetus. The accuracy was found to be best in early measurements (+/-6 days at 7 weeks -+/-11 days at 20 weeks). In regard to clinical decisions reading errors have to be taken into consideration. To avoid them control examinations should be carried out.