Ultrasound features of normal early pregnancy development.

Recent advances in ultrasound imaging have improved the assessment of early pregnancy development. The gestational sac can be detected within the uterine cavity as early as 4 weeks and 3 days after the last menstrual period. High resolution images of early embryos have enabled ultrasound studies of normal brain, abdominal wall or limb development. The definition of standard developmental morphological features may open the possibility of screening for structural defects early in the first trimester of pregnancy.