Green J J, Hobbins J C
Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, CT 06510.
Am J Obstet Gynecol. 1988 Jul;159(1):165-75. doi: 10.1016/0002-9378(88)90515-7.
The first-trimester fetus can now be comprehensively studied with ultrasound. Various biometric measurements correlate well with gestational age, such as crown-rump length (r2 = 0.938) and cranial apex to ear diameter (r2 = 0.983). On the other hand, yolk sac diameter (r2 = 0.129) and abdominal perimeter (r2 = 0.58) correlate poorly with gestational age. By 10 weeks' gestation, kidneys can be visualized in 60% of cases; 98% will be seen at 11 weeks; and 100% of cases will be visible by 12 weeks. The bladder appears later, and by 12 weeks' gestation this organ can be identified in 50% of cases. It is likely that renal agenesis can be diagnosed (or excluded) reliably in the first trimester. With improving technology, prenatal diagnosis of some fetal anomalies is now possible in the first trimester.
