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.
Alternate names for the study include second trimester anatomy scan, fetal anomaly scan or TIFFA (targeted imaging for fetal anomalies).
Second trimester calculation of EDD based on these parameters has a generally accepted error margin of +/- 7 days.
The following structures should be visualised at a routine second trimester morphology ultrasound.
- fetal skull: integrity and shape
- fetal brain:
- profile and nasal bone
- orbits and lenses
- upper lip and palate
Fetal heart and chest
- fetal heart rate and rhythm
- cardiac situs
- four chamber view
- outflow tract views
- aortic and ductal arches
- diaphragm and lungs
- stomach (including situs)
- kidneys and renal arteries
- abdominal wall
- umbilical cord insertion
- bladder and umbilical arteries
- presacral space
- fetal gender
Fetal musculoskeletal system
- 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: saggital views to demonstrate orientation of the ankles to screen for talipes.
- both feet
- fetal lie
- cervical length
- distance to cervix
- liquor volume
- umbilical cord including the number of cord vessels and evaluation of knots
Second trimester of pregnancy
- fetal biometry
- fetal morphology assessment
- soft markers
- 1. Document from the Fetal medicine foundation : - www.fetalmedicine.com/fmf/18-23_Weeks_Scan.pdf
- 2. Document from SOGC Canada : - http://www.sogc.org/guidelines/documents/gui223CPG0903.pdf
- 3. Document of RCOG : - http://www.rcog.org.uk/womens-health/clinical-guidance/ultrasound-screening
- 4. Bethune M et al. A pictorial guide for the second trimester ultrasound. AJUM August 2013; 16 (3):98-113.