Module 7: 2nd And 3rd Trimester Biometry Flashcards
For 2nd and 3rd trimester measurements what are the routine measurements? 7
- Biparietal diameter (BPD)
- Head circumference (HC)
- Abdominal circumference (AC)
- Femur length (FL)
- Humerus Length (HL)
- Occipital frontal diameter (OFD)
- Cephalic index (CI)
How accurate is Biparietal diameter compared to other 2nd trimester dating?
The most accurate measurement in the 2nd trimester for dating a pregnancy
Can we use Biparietal diameter measurements in the 1st trimester?
Yes
When can we use the Biparietal diameter (BPD)?
+/- 7 days on early 2nd trimester
What are some BPD landmarks? 3
- Falx cerebri
- Thalami in the middle of the brain
- Cavun septi pellucidi
The BPD land marks are what kind?
Intracranial landmarks
What is the Falx cerebri? 2
- Fibrous structure that separates the cerebral hemispheres
- Visualized as a horizontal line - anterior to posterior
What is the thalami in the middle of the brain?
Paired hypoechoic structures that appear heart- shaped and lie on either side of the 3rd ventricle
What kind of landmark is the Cavum septi pellucidi? What does it look like?
- Anterior landmark in the brain.
- Hypechoic box
What is the blue box?
Cavum Septi Pellucidi
What do we need to remember about getting the CSP?
Make sure that we don’t get the box not the equal signs.
What is the BPD measurement criteria? 4
- Perpendicular to Falx (as possible)
- Symmetric hemispheres
- Measure at the widest point across the skull
- Calibres placed from outer bone edge to inner bone edge on the opposite side
leading edge to leading edge
What does leading edge to leading edge look like?
Label the structures
- Anterior horn of lateral ventricle
- 3rd ventricle
- Anterior occipital horn with choroid plexus (closest to transducer)
- Posterior occipital horn with choroid plexus (farthest from
transducer)
What are some BPD pitfalls? 3
- Head not perpendicular
- Cerebellum
- CSP not well seen
Label the structures
- The Falx is the structure that separates the straight line
- The CSP is the box
- The Thalami is the farthest left box
Where is the Head circumference (HC) measurement taken? What kind of caliper is used? How should we use it?
- Measured at the same level as the BPD
- Measured with an ellipse calliper
- Eclipse should be placed tightly around the outer skull (do not include skin)
What kind of landmarks are we looking for in terms of the Head Circumference?
Same landmarks as BPD
Occipital frontal diameter (OFD) can be done in conjunction with what?
BPD
OFC is obtained at what level?
Same level as BPD
How should measure OFD?
Measure from outer margin of the frontal bone to the outer marginal of the occipital bone
BPD and OFD are used to calculate what?
Cephalic index (CI)
What is the formula for Cephalic index (CI)?
CI = (BPD/OFD)(100)
What is the normal range for Cephalic index?
75% to 85%
The BPD is considered accurate for determining fetal age if the Cephalic index falls within range