The objective of this study was to determine the optimal gestational age for examining fetal anatomy and nuchal translucency in the first trimester. In a prospective cross-sectional study, 1288 women from an unselected population underwent a detailed assessment of fetal anatomy at 10–14 weeks of gestation (confirmed by crown-rump length) with the use of transabdominal sonography and transvaginal sonography, when necessary.
Visualization of fetal anatomy improved with increasing gestational age: 6, 75, 96, and 98% of cases could be visualized at 10, 11, 12 and 13 weeks of gestation, respectively, and was similarly high (98%) at 14 weeks. The ability to measure nuchal translucency was similar from weeks 10 to 13 (100, 98, 98 and 98% success rate), but fell to 90% at 14 weeks. The need for transvaginal sonography steadily decreased with increasing gestational age, being 100, 42, 21, 15 and 11% at 10, 11, 12, 13 and 14 weeks, respectively. From these data it appears that the optimal gestational age to examine fetal anatomy and measure nuchal translucency in the first trimester is 13 weeks. Copyright © 1998 International Society of Ultrasound in Obstetrics and Gynecology