Introduction

The introduction of diagnostic ultrasound into clinical practice 40 years ago provided a new safe and non-invasive method for in vivo studies of early pregnancy development. The initial studies primarily focused on biometrical descriptions of early pregnancy, while later work was more concerned with normal and abnormal morphological features of embryos and early fetuses. Major improvement in the ultrasound assessment of early pregnancy came with the introduction of transvaginal ultrasound at the end of the 1980s. High-frequency transvaginal transducers improved the image quality to such an extent that a detailed description of the embryonic morphology became possible with in-depth anatomical studies of the brain compartments, the spine, the heart, the stomach, the midgut herniation and the limbs.

Ultrasound examination of the embryo and early fetus

There are three main characteristics that mark the early human conceptus: its small size, its rapidly changing anatomical appearance and its uniform development and constant growth (Figure 13.1). The size of the young human conceptus in the first trimester puts high demands on image resolution. It is therefore important to get as close as possible to the target: use the transvaginal approach instead of the transabdominal route and use high-frequency transducers such as 7.5 MHz or more. With the transvaginal approach, acoustic noise (phase front aberrations and reverberations) and attenuation are reduced, thus improving the image resolution.

Standardisation of the orientation of the images is an important process in improving the diagnostic quality.