A randomized clinical trial (RCT) noted that sonographic examination in the third trimester, in conjunction with delivery at term for abnormalities of fetal growth, significantly decreased the likelihood of small-for-gestational-age (SGA) neonates in uncomplicated pregnancies. We identified 15 characteristics of screening tests and attempted to determine if there is evidence to routinely obtain sonographic estimates of fetal weight in the third trimester and decrease rates of SGA. Of the 15 suggested characteristics, currently 10 (67%) are fulfilled, two are uncertain (sonographic examination is cost-effective or reliable), and one (the test must do its job) is possibly valid. Due to the lack of RCTs demonstrating reduction in morbidity, there is potential for lead-time and length bias. To observe a 36% decrease (from 4.1 to 2.6%) decrease in composite perinatal morbidity, 6000 women need to be randomized to at least two sonographic examinations in the third trimester versus routine prenatal care. Such an RCT is warranted and justified.
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