BIPARIETAL DIAMETER (BPD)

Biparietal
Diameter (BPD) = widest transverse diameter of the fetal head.
Landmarks
 Axial plane through the fetal
head at an angle of about 40° to the
canthomeatal line (suboccipital
bregmatic axis).
 Central landmarks
 Falx
cerebri anteriorly
and posteriorly.
 Cavum
septi pellucidi
midline anteriorly.
 Cerebral peduncles.
 Lateral landmarks
 Anterior horns of
lateral ventricles.
 Hypoechoic
thalami.
 Choroid
plexus of the lateral ventricles.
 Insula,
midway between thalamus and calvarium (middle
cerebral artery pulsation within it).


Skull has an ovoid shape and the Biparietal
Diameter (BPD) is 8090% of the Occipitofrontal
Diameter (OFD)

Measurement
 Adjust gain settings so near
field skull table measures 35mm.
 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).
 Sabbagha
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 2026 weeks when
variability in dates is small. The second BPD will differentiate the
specific cephalic subgroup and should be obtained between 3033 weeks.
This method of assigning a growth adjusted sonographic
age (GASA) reduces variability in the estimates of dates.
Biparietal diameter
(BPD) (Table) – Chervenak et.al
1992
Biparietal diameter (BPD) (Table) – Hadlock et.al. 1984
Biparietal diameter (BPD) (Table) – Romero et.al. 1988
Biparietal diameter (BPD) (Graph) – Chervenak
et.al 1992
Biparietal diameter (BPD) (Graph) – Hadlock et.al. 1984
Biparietal diameter (BPD) (Graph) – Romero et.al. 1988
Variability

( +/ 2SD)

1218 wks
1824 wks
2430 wks
3036 wks
3642 wks

+\ 1.2 wks
+\ 1.7 wks
+\ 2.2 wks
+\ 3.1 wks
+\ 3.2 wks

Precision of predictors of
Gestational Age
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
FOD/1.265.
 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.
 Sabbagha
re, Barton DA, Barton FB et.al. Sonar
biparietal diameter: II. Predictive of three fetal growth patterns
leading to closer assessment of gestational age and neonatal weight. Am J
Obstet Gynecol 1976;126:485490.