Second trimester ultrasound scan

Last revised by Dr Jeremy Jones on 20 Sep 2021

The second trimester scan is a routine ultrasound examination in many countries that is primarily used to assess fetal anatomy and detect the presence of any fetal anomalies. 

The second trimester extends from 13 weeks and 0 days to 27 weeks and 6 days of gestation although the majority of these studies are performed between 18 and 23 weeks.

Terminology

Alternate names for the study include second trimester anatomy scan, fetal anomaly scan or TIFFA (targeted imaging for fetal anomalies).

Radiographic features

Biometry

The following measurements are routinely obtained to calculate estimated fetal weight (EFW) and estimated date of delivery (EDD):

Second trimester calculation of EDD based on these parameters has a generally accepted error margin of +/- 7 days.

Morphologic assessment

The following structures should be visualized at a routine second trimester morphology ultrasound.  

Fetal head
Fetal face
  • profile and nasal bone 
  • orbits and lenses
  • upper lip and palate
  • mandible
Fetal heart and chest
Fetal abdomen
Fetal musculoskeletal system
  • spine
    • transverse, longitudinal +/- coronal views and skin line
  • upper limb
    • humera, including humeral length (HL)
    • radius/ulna: both sides
    • fingers and thumbs, including hand opening
  • lower limb
    • both femora, including femoral length (FL) as part of biometric assessment
    • both tibia/fibula: sagittal views to demonstrate orientation of the ankles to screen for talipes.
    • both feet
Ancillary findings

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Cases and figures

  • Case 1: normal biometry
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  • Case 2: normal biometry
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