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This article has essentially been a list of secondary factors for selecting an ultrasound machine. When a clinician narrows his/her choices for a new machine by viewing the image quality and features, the secondary factors in this article also should be studied. By doing so, a number of traps will be avoided and complaints from staff will be decreased. All sonographers and staff should have input to machine selection because all may have an impact on office operations. By anticipating problems before they occur, the selection of a new ultrasound machine becomes a smooth, well defined operation.

Recent developments in both laboratory measurements and ultrasound technology have revolutionized the management of early pregnancy. The discriminatory zone concept is a direct result of these developments. By correlating the serum beta-hCG values to the size of an intrauterine gestational sac, a value can be chosen that corresponds to the threshold of visualization of the sac. If the beta-hCG is above this value, a sac must be seen, and if it is not, aggressive steps should be taken to determine whether the pregnancy is abnormal or ectopic. The discriminatory zone may vary among institutions due to different equipment and assays. Thus, its value should be calculated individually at each institution. A proper discriminatory zone and a management protocol such as the one above can eliminate much of the uncertainty in the management of suspected ectopic and early pregnancies.

A multiple regression-based statistical model capable of quantitatively comparing two or more sonographic parameters for the effects of gestational age, variation in fetal growth and error in sonographic measurement is presented and then used to compare the biparietal diameter and femur length as estimators of gestational age in late pregnancy. A total of 311 patients were studied between 24 and 42 weeks' gestation. Variation in fetal growth was expressed as the birth weight percentile for gestational age. Biparietal diameter and femur length correlated equally well with gestational age. However, the biparietal diameter was more than twice as sensitive as the femur length to variation in fetal growth. Femur length had a larger error associated with its measurement. These results suggest that the biparietal diameter and femur length in late pregnancy are equal estimators of gestational age; that the femur length is a more stable estimator of gestational age when fetal growth deviates from normal; and that the femur length is technically more difficult to obtain.