When taking images the structure of interest should occupy about 75% of the screen to maximise resolution. A separate pre‐set with higher frame rates and higher contrast is useful for cardiac images. Many machine pre‐sets are a compromise of resolution and persistence and it is important to have a high resolution pre‐set available. Operators would benefit from a systematic approach to ensure that all structures are seen even in difficult circumstances, as it can be possible to miss a structure, especially when there are active fetal movements. This guide is presented roughly in cephalic to caudal order, but where possible grouped by organ system. Although the important features are described it is beyond the scope of this article to discuss the associated pathologies of each feature. Rather, we are suggesting that each labelled landmark is worth examining carefully during a second trimester ultrasound. The authors are not suggesting that an examination is only complete if all of these images are presented.
Some examinations may yield significantly better images while other examinations, especially in large patients, may yield much less clear images. These images were all obtained on GE Healthcare Voluson E8 or 730 machines (GE Healthcare, Sydney, Australia). This pictorial guide is provided as, despite a large volume of literature on the subject, it is difficult to find a single publication that describes the landmarks and range of images which are most useful to look for when performing the second trimester ultrasound.
In order to maximise detection rates there is evidence that the ultrasound should be performed by operators with specific training in the detection of fetal abnormalities. The second trimester ultrasound is now less often required for dating or detection of multiple pregnancies but remains very important to detect placental pathology and, despite advances in first trimester anomaly detection, remains an important ultrasound for the detection of fetal abnormalities. Many patients now have several ultrasounds in their pregnancy with the first trimester nuchal translucency assessment becoming particularly common. Historically the second trimester ultrasound was often the only routine scan offered in a pregnancy and so was expected to provide information about gestational age (correcting menstrual dates if necessary), fetal number and type of multiple pregnancy, placental position and pathology, as well as detecting fetal abnormalities.
The second trimester ultrasound is commonly performed between 18 and 22 weeks gestation.
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