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Introduction to the 2T US ATLAS

2T US Atlas Table of Contents


The goal of this atlas is to provide a quick resource that you can easily access on your computer or phone to help assess what is ‘normal’.  Before moving on to diagnose what is ‘abnormal’, it is vital to be confident with what ‘normal’ fetal anatomy looks like during the second trimester scan. 

While different countries may have different standards for timing of the 2nd trimester ultrasound.  Biometry algorithms may likewise be dissimilar. But fetal anatomy is universal. 

Aside from the brief summaries and ‘tips’, scroll down and you will find The ObG Project entries related to structures being reviewed, including current guidelines.  Tap key words for helpful glossary terms.

What Does ‘Normal’ Mean?

Even in the best of hands, structural anomalies can be missed.  It is always important to let a patient know that birth defects can occur in 3 to 4% of pregnancies and many, but not all abnormalities, can be detected on ultrasound.  Sometimes the problem is simply too small to see, while some defects may not develop until later in the pregnancy.

The Key ‘Take Home’ Point 

If ever there is the slightest doubt as to whether an image is ‘normal’, consider referral to a center with expertise in fetal ultrasound to confirm whether there is a structural abnormality, and if so, to make a diagnosis quickly.  You can find helpful resources, including where to find a maternal fetal medicine expert (US) and genetic services (US and Canada).

Special Thanks To  

Sina Haeri MD, MHSA, FACOG for providing ‘Key Points’ and highlights. 

Learn More – Primary Sources:

AIUM Practice Parameter for the Performance of Limited Obstetric Ultrasound Examinations by Advanced Clinical Providers

Consensus Report on the Detailed Fetal Anatomic Ultrasound Examination

Obstetric and gynecologic ultrasound curriculum and competency assessment in residency training programs: consensus report 

ISUOG Practice Guidelines (updated): sonographic screening examination of the fetal heart

AIUM Practice Parameter for the Performance of Obstetric Ultrasound Examinations

ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan

Locate a Genetic Counselor or Genetics services:

Genetic Services Locator-ACMG

Genetic Services Locator-NSGC

Genetic Services Locator-CAGC

Locate a Maternal Fetal Medicine Specialist:

Maternal-Fetal Medicine Specialist Locator-SMFM

We acknowledge Bethune M, Alibrahim E, Davies B, Yong E., A pictorial guide for the second trimester ultrasound. Australasian Journal of Ultrasound in Medicine. 2013;16(3):98-113. doi:10.1002/j.2205-0140.2013.tb00106.x. Published by John Wiley and Sons