[Fetal femur length in the 2d and 3d trimester of pregnancy].

Results of sonographic determination of the length of femur between the 12th and 42nd week of pregnancy are presented. The length of femoral diaphysis was determined as part of a cross-sectional study on a total of 595 patients who were not at risk, and where the gestation age was known and confirmed. The growth function of the foetal femoral length was determined via a polynomic regression equation. The foetal femoral length growth presents a characteristic appearance between the 12th and 42nd pregnancy week. In the 12th pregnancy week it is 11 mm on the average, 33 m in the 20th, 58 mm in the 30th, and 76 mm at birth. After an almost linear progression up to about the 30th week of pregnancy, the growth curve gradually begins to flatten out from that time. The mean growth rate of foetal femoral length during the entire period under observation is about 1 to 3 mm per pregnancy week. The authors present a table showing the 95% interval for estimating the gestational age. A relatively accurate estimate of the gestational age is particularly possible in the "early" range between 5 and 32 mm (corresponding to the 12th to 20th week of pregnancy), namely, +/- 9.7 to 10.3 days (95% interval). In femoral measurement results 33 mm to 76 mm (corresponding to the 20th to 42nd week of pregnancy), the range of error of the estimate is +/- 20.6 days. Additional measurement of the foetal femoral length is useful for on-target diagnosis of malformations, for estimating the gestational age, for growth control/weight estimation, and, in certain cases, also for diagnosing the maturity.