Dating & Growth Percentiles in 2nd & 3rd trimester

---

In the second and third trimesters, fetal growth is assessed using biometric parameters including:

Biparietal Diameter (BPD)

Head Circumference (HC)

Abdominal Circumference (AC)

Femur Length (FL)

Estimated Fetal Weight (EFW)

These values are plotted against gestational age-specific percentile charts, which help determine whether the fetus is growing normally.

Biparietal Diameter (BPD)

Measurement Method:
Plane:
Axial (transverse) plane of the fetal head at the level of:
- Thalami
- Cavum Septi Pellucidi (CSP)
- Third ventricle

Technique:
- Ensure head is oval and symmetrical.
- Midline falx should be equidistant from both skull bones.
- Calipers should be placed from the outer edge of the near skull (proximal) to the inner edge of the far skull (distal).
- This is known as the “outer-to-inner” method.
Optimal View Criteria:
- Head should appear round or oval (not compressed or elongated).
- Midline falx should be clearly visible and centered.
- CSP should be seen anterior to the thalami.
- Avoid oblique sections or pressure-induced distortion.
Best Time to Measure:
- From 13+ weeks gestation onward, most reliable during the 2nd trimester.
Pitfalls to Avoid:
- Do not include orbits (too low) or skull vault (too high).
- Avoid oblique angles or compression by uterine wall or limbs.
- Consider using Head Circumference (HC) if skull shape is abnormal.

---

Head Circumference (HC)

Measurement Method:
Plane:
Axial (transverse) plane of the fetal head at the level of:
- Thalami
- Cavum Septi Pellucidi (CSP)
- Third ventricle

Technique:
- Ensure a symmetrical, oval cross-section of the fetal head.
- Use the ellipse tool to trace the outer edge of the skull bone (outer-to-outer).
- Calipers must not include scalp or soft tissues.
Optimal View Criteria:
- Midline falx is centered and equidistant.
- CSP visible anterior to thalami.
- Head shape is oval, not round or compressed.
Best Time to Measure:
- After 13+ weeks gestation, especially reliable in the 2nd trimester.
Pitfalls to Avoid:
- Avoid measuring in oblique sections.
- Do not include skin or scalp in circumference.
- Prefer HC over BPD in cases of dolichocephaly or brachycephaly.

---

Abdominal Circumference (AC)

Measurement Method:
Plane:
Axial (transverse) view of the fetal abdomen at the level of:
- Stomach bubble
- Left portal vein (hockey stick or J-shaped configuration)
- Umbilical portion of the left portal vein

Technique:
- Ensure the abdomen is round and symmetrical, not oval or distorted.
- Use the ellipse tool to trace along the outer skin edge (skin-to-skin).
- Do not include the ribs or spine prominence in measurement.
Optimal View Criteria:
- Stomach bubble and portal sinus are clearly visible.
- Spine is at a lateral position (ideally between 3 to 5 o’clock or 7 to 9 o’clock).
- No obliquity or compression of the fetal abdomen.
Best Time to Measure:
- Most reliable in the second and third trimesters for fetal weight estimation.
Pitfalls to Avoid:
- Avoid measuring in oblique or distorted planes.
- Do not include subcutaneous tissue excessively or exclude the skin edge.
- Avoid measurement during fetal movement or respiration.

---

Femur Length (FL)

Measurement Method:
Plane:
Longitudinal view of the femur (preferably the femur closest to the probe).

Technique:
- Align the transducer to obtain a straight, unforeshortened view of the entire femoral diaphysis.
- Measure only the ossified diaphysis (bone shaft).
- Exclude femoral head epiphysis and distal cartilaginous ends from the measurement.
- Calipers should be placed at the outer margins of the ossified diaphysis (outer to outer).
Optimal View Criteria:
- Bone appears straight and clearly visualized without curvature.
- Ends of the diaphysis should appear sharp, not fuzzy or oblique.
Best Time to Measure:
- From the second trimester onwards, reliable for dating and fetal growth assessment.
Pitfalls to Avoid:
- Avoid measuring a foreshortened femur (due to oblique angle).
- Do not include the cartilaginous epiphysis in the measurement.
- Use only the femur clearly visible and properly aligned — not the shadowed opposite side.

---

Estimated Fetal Weight (EFW)