Biparietal diameter

Last revised by Dr Jeremy Jones ◉ on 20 Sep 2021

Citation, DOI and article data

Citation:

Stanislavsky, A., Jones, J. Biparietal diameter. Reference article, Radiopaedia.org. (accessed on 22 Oct 2021) https://doi.org/10.53347/rID-26429

DOI:

https://doi.org/10.53347/rID-26429

Permalink:

https://radiopaedia.org/articles/26429

rID:

26429

Article created:

21 Dec 2013 by Dr Alexandra Stanislavsky ◉

Revisions:

19 times by 5 users - see full revision history

System:

Obstetrics

Section:

Tag:

stub, ultrasound, fetal head

Synonyms:

Biparietal diameter (BPD)
BPD

Biparietal diameter (BPD) is one of the basic biometric parameters used to assess fetal size.

BPD together with head circumference (HC), abdominal circumference (AC), and femur length (FL) are computed to produce an estimate of fetal weight. In the second trimester this may be extrapolated to an estimate of gestational age and an estimated due date (EDD).

Measurement technique

The BPD should be measured on an axial plane that traverses the thalami, and cavum septum pellucidum. The transducer must be perpendicular to the central axis of the head, and thus the hemispheres and calvaria should appear symmetric.

The calipers should be placed at the:

outer edge of the near calvarial wall
inner edge of the far calvarial wall

The cerebellar hemispheres should not be in the plane of the image.

Interpretation

BPD has been shown to be accurate in predicting gestational age from 14 to 20 weeks ². The variability increases after this time. BPD may also be influenced by factors such as abnormalities of head shape, breech presentation, or multiple gestations. Head circumference (HC) may be a more reliable measurement if there is variant head shape ⁴.