Application of obstetric ultrasound to determine the most suitable parameters for the aging of formalin-fixed human fetuses using manual measurements.

The aim of this study was to find the most suitable manual measurements to estimate the age of preserved fetuses. A new technique was used to make successful ultrasonic measurements on 86 out of 100 preserved fetuses under conditions simulating the intrauterine environment. The ultrasonographic images of the preserved specimens were very similar to those of live fetuses. Ultrasonic measurements of standard parameters, and the ages derived from them, were computed directly by the ultrasound scanning machine. Manual measurements were made of the same parameters using established techniques and standard tables for estimating fetal age. The measurements and the ages obtained for each parameter by the two techniques were statistically compared using the limits of agreement (Bland and Altman, 1986). Of the manual measurements used in the estimation of fetal age, foot length was found to be the most suitable parameter for practical use. Biparietal diameter was equally good, but the head circumference was the most precise, especially when used in conjunction with the formulae developed for ultrasonic measurements. Crown-rump length was found to be unsuitable to age fetuses beyond the first trimester due to distortion of the spine caused by compression in storage.