Embryosonology in the First Trimester of Pregnancy

In the early days of ultrasound, documentation of developmental milestones in the first trimester was limited by the transabdominal approach through a distended urinary bladder. Depiction of the rapid growth and development of the embryo only became possible with the advent of transvaginal sonography in the early 1980s. With better resolution came a clearer correlation between normal embryologic events and ultrasound image displays. Sonographers and sonologists need a clear understanding of the normal sequence of events to distinguish them from abnormal findings. Avoiding pitfalls in diagnosis is necessary to guide management decisions in a patient who presents with first trimester complications.