BACKGROUND

The Basic Training Sub-Committee (BTSC) of the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) was established in 2013 with the aim of creating a Basic Training (BT) program to support newly qualified or qualifying professionals entering the field of ultrasound in obstetrics and gynecology. Upon successful completion of the BT program, trainees can perform independently an obstetric and gynecological ultrasound examination and are competent to recognize potential structural abnormalities, which require referral for a second opinion¹.

Performing the routine second-trimester anomaly scan correctly is part of the BT obstetrics teaching program. The planes and measurements required for this scan have been defined in the ISUOG Practice Guidelines^2-7. However, one of the difficulties faced by the ultrasound student or the newly qualified practitioner is understanding, and being able to apply, the correct qualitative and/or quantitative criteria when deciding whether the part of the fetal anatomy being examined, and/or its size, is ‘normal’ for the gestational age at which the scan is being performed.

We have designed the 20 + 2-planes method as a practically focused addition to the BT program, and to provide a logical, comprehensive and time-efficient approach to the routine second-trimester scan in accordance with ISUOG guidelines. This method incorporates the tools required to make clinically relevant decisions. It thus helps to develop the confidence needed by the trainee and/or newly qualified practitioner to determine which findings require referral to a more experienced colleague following a routine second-trimester anomaly scan, and which do not.

The structures requiring examination (of which some also require measurement) within each of the 20 planes in the 20 + 2-planes method are described herein. Members of the original ISUOG BTSC reviewed these data to agree: (1) qualitative and quantitative criteria for referral and (2) a list of common fetal anomalies that this method, when followed correctly, should exclude. Referral criteria relating to measurements were then agreed by the BTSC and were based either on internationally accepted published data or, when these were not available, on consensus within the group. In accordance with ISUOG guidelines, no recommendations are made as to which biometry charts should be used for reference, these being a matter of local and/or national preference^1, 8.

Herein, we provide an overview of the 20 + 2-planes method and how its correct application during a routine second-trimester fetal ultrasound examination assists in the identification or exclusion of 65 fetal structural anomalies. This How To document is intended to reflect best practice at the time of publication. It is not intended to establish a legal standard of care because some deviations are inevitable depending on individual circumstances and available resources.