BIPARIETAL DIAMETER (BPD)
Diameter (BPD) = widest transverse diameter of the fetal head.
- Axial plane through the fetal
head at an angle of about 40° to the
cantho-meatal line (suboccipital
- Central landmarks
- Cerebral peduncles.
- Lateral landmarks
- Anterior horns of
plexus of the lateral ventricles.
midway between thalamus and calvarium (middle
cerebral artery pulsation within it).
Skull has an ovoid shape and the Biparietal
Diameter (BPD) is 80-90% of the Occipitofrontal
- Adjust gain settings so near
field skull table measures 3-5mm.
- Measure from outer surface of
the skull table in the near field to the inner margin of the skull table
in the far field(outer to inner).
et.al. (1) have
classified BPD growth into three subgroups: large, average and small. Two
BPD measurements should be obtained to place a fetus in a specific
cephalic subgroup. The first BPD is best measured between 20-26 weeks when
variability in dates is small. The second BPD will differentiate the
specific cephalic subgroup and should be obtained between 30-33 weeks.
This method of assigning a growth adjusted sonographic
age (GASA) reduces variability in the estimates of dates.
(BPD) (Table) – Chervenak et.al
Biparietal diameter (BPD) (Table) – Hadlock et.al. 1984
Biparietal diameter (BPD) (Table) – Romero et.al. 1988
Biparietal diameter (BPD) (Graph) – Chervenak
Biparietal diameter (BPD) (Graph) – Hadlock et.al. 1984
Biparietal diameter (BPD) (Graph) – Romero et.al. 1988
( +/- 2SD)
+\- 1.2 wks
+\- 1.7 wks
+\- 2.2 wks
+\- 3.1 wks
+\- 3.2 wks
Precision of predictors of
Disadvantage of BPD is that it disregards the shape of the cranium. i.e. two heads of equal widths but different lengths will
have the same BPD's, but the longer head will have a
greater corrected BPD or HC than the shorter head.
- Shape corrected BPD = BPD x
- When this shape correction is
performed the BPD is equivalent to the head circumference, as a predictor
of menstrual age as is becomes shape independent.
re, Barton DA, Barton FB et.al. Sonar
bi-parietal diameter: II. Predictive of three fetal growth patterns
leading to closer assessment of gestational age and neonatal weight. Am J
Obstet Gynecol 1976;126:485-490.