First trimester ultrasound for fetal structure
This ultrasound is done early in the pregnancy at 11-13 6/7 weeks to assess for major or serious fetal structural abnormalities. Many patients would like to know if their pregnancy is “healthy” as soon as possible, especially before making announcements to friends, family, or their employer. While this ultrasound cannot always detect subtle differences in fetal structure, it is able to detect major issues which may be lethal or have adverse effects on the mother’s health.
The detailed obstetric ultrasound examination in the late first trimester is an indication- driven examination for women at increased risk for fetal or placental abnormalities. Approximately 50% of major anomalies are detected in this gestational age window.
First trimester ultrasound anatomical survey does not replace a second trimester detailed exam. All structures imaged today will need to be reevaluated during future studies.
These early anatomical surveys are helpful to assess global issues or obvious problems but that even if a structure is felt to be "normal" at this gestational age, it will need more detailed evaluation later and new findings may appear. The first trimester ultrasound is done to rule out major lethal anomalies as early as possible in the gestation.