How to measure bpd on ultrasound?

Above.  Crown rump length at 11 weeks.

The first trimester crown rump length (CRL) is the most accurate method to determine gestational age and once established should not be changed.  The CRL is defined as the longest embryo length excluding the limbs and yolk sac.  It is the measurements between the top of the head to the distal sacral area.

Above.  Note the increased CRL with advancing gestational age.

Above.  CRL versus gestational age courtesy of:  “Medical Gallery of Mikael Häggström 2014,” Wikiversity Journal of Medicine.

AGE             CRL

6.1 Weeks:  0.4 cm 7.2 Weeks:  1.0 cm 8.0 Weeks: 1.9 cm 9.2 Weeks:  2.5 cm 9.5 Weeks:  2.9 cm 10.5 Weeks:  4.0 cm 12.1 Weeks:  5.5 cm 13.2 Weeks:  6.90 cm 14.0 Weeks:  8.0 cm

Above.  Typical gestational age compared to CRL measurement in cms.  Source courtesy of:  Wikipedia

Beginning at 13 to 14 weeks gestation the biparietal diameter (BPD), the head circumference (HC), the abdominal circumference (AC), and femur length (FL) should be measured.

Reference Values

Reference values for biometry from 14 to 40 weeks can be obtained from the citation [1], which can be viewed at:

http://onlinelibrary.wiley.com/doi/10.1046/j.1469-0705.1994.04010034.x/pdf

In order to measure the BPD and HC, the transthalamic plane must be imaged. [2]

Above.  This is the same acquisition plane for the BPD and HC.  Visualization of the thalami, the midline falx, and the box-like cavum septi pellucidi (CSP) are possible.  The presence or absence of the CSP is a key factor in defining abnormal brain anatomy.

1.  The BPD can be measured through any plane that crosses the 3rd ventricle, thalami, and cavum septi pellucidi (CSP).

2.  The calvaria should be smooth and symmetrical as indicated.

3.  The cursor in the near field should be placed on the outer edge of the calvaria and the cursor in the far field should be placed on the inner edge as indicated.

Above.  For the HC measurement:

1.  Measurement is through a plane that crosses the 3rd ventricle, thalami, and CSP. 2.  The calvaria should be smooth and symmetrical. 3.  The cavum septi pellucidi (CSP) should be visible in the anterior portion of the brain. 4.  Caliper placement is around the calvarial wall and should not include scalp thickness.

Above.  The CSP appears as a box like structure in the anterior portion of the brain as demonstrated.  The hyperechoic lines represent the medial walls of the lateral ventricle.

Above.  The 3-lined structure is not the CSP and represents the columns of the fornix.  The fornix represents paired nerve columns, which are located just inferior to the CSP.  The transaxial view when the fornix is seen suggests that the transducer plane is just inferior to the proper plane to obtain the CSP.

Above.  Note the difference between the box like structure, the CSP, and the structure with 3 parallel lines, which represent the columns of the fornix.

The CI is an index or ratio which is used to evaluate the shape of the head.  It is calculated by measuring the maximum width (BPD) of the cranium divided by its maximum length (occipital frontal diameter, OFD).  The front to back, OFD, is measured with the cursor placed on the outer edge to outer edge of the cranial bones as demonstrated.  The following formula derives the cephalic index:

CI =BPD/OFD x 100

A normal cephalic index (CI) = 78.3%  [6787895-refs key=”key” limit=number]

1 Standard Deviation (SD) = 74%-83%

2 Standard Deviations (SD) = 70%-86%

Above.  Dolicocephaly is defined when the AP diameter is longer than the transverse diameter and the CI is <70% (> 2 SD).  Dolicocephaly may be seen in a number of conditions, including oligohydrmnios and multiple gestations.

Above.  Brachycephaly is defined when the transverse diameter is greater than the AP (anterior posterior) diameter and the CI is > 86% (> 2 SD).  Brachycephaly may be seen in a number of conditions including synostosis, trisomy 21, and hydrocephalus.

Above.  The AC measurement should be taken at the skin line on a true transverse view at the level of the junction of the umbilical vein, portal sinus, and fetal stomach.  At this location, the liver size is reflected.  The visualized ribs should be symmetrical.  The abdomen should not be compressed during image acquisition.

Above.  Correct AC measurement.  Note placement of cursor outside skin line.  Again, ribs are symmetrical.  The stomach is seen and both the umbilical vein and portal sinus are identified.

Above.  Incorrect imaging of AC.  Note that the portal sinus is not seen, the rib images are not symmetrical, and the stomach is not well visualized.

Above.  Incorrect imaging of AC.  The liver is visualized, but the portal sinus is not well defined.  The rib images are not symmetrical and the stomach is not well visualized.

Above.  Incorrect imaging of AC.  The liver is visualized, but the umbilical vein is not seen and the portal sinus is not well defined.  The kidney should not be in the field of view.  The stomach is seen but not in relationship to the umbilical vein or portal sinus.

Above.  The long axis of the diaphysis of the femur is most accurately measured when the ultrasound beam of insonation is perpendicular to the shaft.  The cartilage at the ends of the femur should not be included in the measurement.

Above.  Only the diaphysis should be measured between the epiphysis, which represents the portion of the long bone formed by the primary ossification center.

Above.  Note the femoral head which is distinct from the femoral epiphysis.

Above.  The principles of HL measurement correspond to those of the femur.  The insonation of the ultrasound beam is best directed in a perpendicular fashion and the diaphysis alone is measured after the forearm and shoulder region are identified.

The fetal foot measurement is taken from the tip of the longest toe (typically the second toe) to the tip of the heal. [3] A chart for fetal foot measurements and gestational age is provided at:  http://www.drhern.com/pdfs/corrfetal1026.pdf

Above.  The ulna is longer than the radius.  Note that it extends into the elbow, higher than the radius.  The radius is on the thumb side and the ulna is on the 5th digit or little finger side of the forearm.  Again, the measurement is easier to establish when the ultrasound beam is perpendicular to the long bone.

Among the bones of the lower leg, the fibula is smaller than the tibia.  The tibia is longer than the fibula and the tibia originates closer to the knee compared to the fibula.

Above.  The orbits and the lens of the eye can be viewed when both orbits are in a coronal or axial view and are most easily visualized when the fetal head is in a direct occiput posterior position.

The BOD is measured from the outer edge of one orbit to the outer edge of the other orbit.  These measurements may be useful in assessing certain syndromes, potential karyotype abnormalities, severe growth restriction, or in assessing fetal age when other measurements are difficult to obtain.

The IOD represents the outer edge to outer edge distance between the orbits.  It may be measured for the same reasons that BOD is measured and when facial anomalies are suspected.

Three­-dimensional (3-D) ultrasound compared with magnetic resonance imaging (MRI) in the diagnosis of Müllerian duct anomalies is highly accurate. [4] (This article is an excellent review of certain uterine anomalies.  The full text is available at:  https://obgyn.onlinelibrary.wiley.com/doi/full/10.1002/uog.14825).  After being suspected of a uterine anomaly on two-dimensional scanning, 60 women were evaluated with 3-D ultrasound and with MRI.  Compared with MRI, 3-D ultrasound had a sensitivity of 100% for dysmorphic uteri, and the kappa was 1.00.  For hemi­-uteri, the sensitivity was 100%, and the kappa was 1.00.  For septate uteri, the sensitivity was 100%, and the kappa was 0.918.  For bicorporeal uteri, the sensitivity was 83.3%, and the kappa was 0.900.  Therefore, 3-D ­ultrasound is highly accurate for diagnosing uterine malformations, and it also has a good level of agreement with MRI in the classification of different anomalies.

Among 4000 women who underwent a second trimester scan, a small percentage were incomplete due to unfavorable fetal position. [5] Among the study population, 4.2% returned for a follow-up scan within two weeks.  Only one view was needed in a subsequent scan in 2.6%, while 1.6% required more than one view.  The most difficult organs to visualize during the initial scan were:  corpus callosum (1.8%), fetal face (1.7%), cerebellar vermis (1.1%), and fetal heart (1.0%).

Every human has two parietal bones—one on the left side of the skull and one on the right side. Each parietal bone looks like a curved plate that has two surfaces and four sides.

Imagine taking a string and placing one end at the top of your right ear and the other end at the top of your left ear, letting it rest on top of your head. The length of that string would give you a very rough idea of your biparietal diameter. An ultrasound technician takes this measurement while looking at your developing baby on a computer screen and using digital measuring tools.

The BPD measurement is usually taken during standard ultrasounds in pregnancy. Most people have anywhere from one to three ultrasounds (also known as sonograms), usually from early in pregnancy through about week 20. People who are considered to be at high risk may need more ultrasounds.

A BPD measurement is useful alongside three other measurements:

Those three measurements, taken together, help estimate fetal weight and gestational age (how far along the pregnancy is). The BPD measurement also gives you and your doctor a sense of how your developing baby's brain is growing. Your doctor is looking for the BPD measurement, as well as the other measurements, to be within what is considered normal range.

Taking a biparietal diameter measurement late in pregnancy is not considered to be as reliable in predicting gestational age. Between week 12 and week 26 of pregnancy, BPD tends to be accurate for predicting gestational age within 10 to 11 days. However, after week 26 of pregnancy, it may be off by as much as three weeks. Other studies show that BPD becomes less accurate after week 20.

If your baby's results are outside of a normal range, your doctor may recommend further tests. For instance, if your baby's BPD measurements is smaller than usual, that could be a sign of an intrauterine growth restriction or that your baby's head is flatter than usual. If your baby's BPD measurement is larger than expected, it could signal that a health issue, such as gestational diabetes.

A low BPD can be an indication to monitor fetal head growth. Microcephaly can be a concern for women who may have been exposed to the Zika virus. If the BPD falls two standard deviations below the mean, the head is considered to be excessively flat and microcephaly is suspected. Microcephaly has other indications, such as the appearance of the head and other measurements.

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.

• BPD (biparietal diameter), the diameter of your baby's head.
• HC (head circumference), the length going around your baby's head.
• CRL (crown-rump length), the length from the top of the head to your baby's bottom, measurement taken in the first trimester.