Abdominal ultrasound examination of the first-trimester fetus.
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.
Green
J J
JJ
Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, CT 06510.
Hobbins
J C
JC
D000005:Abdomen / Q000196:embryology; D004622:Embryo, Mammalian / Q000033:anatomy & histology*; D005121:Extremities / Q000196:embryology; D005260:Female; D005333:Fetus / Q000033:anatomy & histology; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011296:Prenatal Diagnosis; D012886:Skull / Q000196:embryology; D013131:Spine / Q000196:embryology; D014463:Ultrasonography; D015017:Yolk Sac / Q000033:anatomy & histology