How to do a second trimester anomaly scan

A systematic evaluation of the fetal anatomy as part of the second trimester ultrasound examination in pregnancy is useful in detecting pregnancy complications, fetal abnormalities, and genetic diseases. We aim to illustrate the basic and detailed second trimester scan, according to current international and national guidelines, as well as to our own every-day practice in the Department for Prenatal Diagnosis at the University of Tübingen, Germany.

Ultrasound examination in pregnancy is one of the main pillars of modern obstetric care. It helps to establish an accurate gestational age and enables a timely detection of pregnancy complications such as fetal structural defects and genetic diseases, multiple gestations, fetal growth restriction, amniotic fluid volume abnormalities, abnormal fetal presentation and abnormal placentation. Timing of the ultrasound examination can be broadly divided into the following categories: a first trimester and a second trimester assessment and, in some settings, a third trimester scan.
The second trimester ultrasound assessment focuses on fetal sonoanatomy to detect fetal structural defects, as well as markers for chromosomal or genetic abnormalities. At present, approximately 50% of all fetal abnormalities are detected prenatally, with detection rates varying widely [1]. For some organ-specific malformations, a structured screening programme has been shown to improve detection rates and outcomes [2]. A Cochrane meta-analysis to assess the effectiveness of second trimester screening in a low-risk population has been initiated [3].
Many scientific societies, among them the ISUOG (International Society of Ultrasound in Obstetrics and Gynaecology) [4], the DEGUM (Deutsche Gesellschaft für Ultraschall in der Medizin) [5] and the AIUM (American Institute of Ultrasound in Medicine) [6], as well as national health authorities, such as the NHS (National Health Service) in the United Kingdom [7], have published guidelines, which define the standard sonoanatomical planes needed for a second trimester fetal examination. In general, national guidelines cover the basic scan requirements. Description of additional views required for a detailed examination is usually provided by scientific societies, which suggest that advanced skills are needed for its performance. This is specifically emphasized in the AIUM guidelines [6].
The ultrasound images below illustrate views, which are required for the completion of a detailed second trimester examination as recommended by ISUOG, AIUM and DEGUM, as well as additional planes and structures that are part of the scanning protocol in the Prenatal Diagnostic Department of the University Clinic for Obstetrics and Gynaecology in Tübingen. We have highlighted the images that are mandatory for the examination according to the ISUOG (*), AIUM (+), DEGUM (#) and NHS-FASP (%) guidelines. We also have marked the additional images that we routinely assess in our clinic as "Tuebingen protocol". These images are not included in the national recommendations. Still, we believe that they provide valuable information for the pregnancy care.
The enclosed series of images were acquired in ideal conditions in patients with low body mass index, fetus in optimal position, normal amniotic fluid, no fibroids and no uterine malformations. They are also obtained in a series of patients. Therefore, we acknowledge that in every-day clinical practice, one may encounter situations where the acquisition of images of such quality is not possible. Still, every attempt should be made to demonstrate all the relevant structures. If this is not possible, it may be necessary to 1 3 gently move the fetus with the other hand, to ask the patient to turn to the side, to send the patient for a walk and to empty the bladder or finally to rebook the patient 2 weeks later for another detailed ultrasound examination. Any limitation that affects image quality should be noted in the report (see Fig. 1).
Author contributions NCP: data collection, manuscript writing and editing. MH: manuscript writing and editing. GJ: manuscript writing and editing. KOK: project conception and development, data collection, manuscript writing and editing.
Funding Open Access funding enabled and organized by Projekt DEAL.

Conflict of interest No competing interests.
Ethics approval No ethical approval was required.

Fig. 1 (continued)
Consent to publication All authors have agreed to publish this manuscript in Archives in Obstetrics and Gynaecology.
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