fetal biometry n.
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Fetal biometry. The common tomograms used : Axial Coronal Sagittal (midline). F etal biometry . Fetal growth can be monitored accurately later in life only if the exact information about the GA is available. As less than 50% of women are certain about their LMP.

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The common tomograms used :

  • Axial
  • Coronal
  • Sagittal (midline)
f etal biometry
Fetal biometry
  • Fetal growth can be monitored accurately later in life only if the exact information about the GA is available.
  • As less than 50% of women are certain about their LMP.
  • Menstrual cycle is not 28days long
  • Irregular
  • Taking COC
  • Women had bleed in early pregnancy
  • Lactating women

Gestational age: length of the pregnancy based upon reliable LMP, assuming that conception occurs 14 days later.

  • Postmenstrual age: the length of pregnancy based on the LMP, irrespective of its reliability.

Several US parameters have been used to estimate GA, the most commonly used are:

Mean sac diameter

Gestational sac volume

Crown rump length

Biparietal diameter

Femur length

crown rump length
Crown rump length
  • The biologic variability of CRL is small & growth is very rapid.
  • However there are still a number of factors that can affect the size of embryo;
  • Measurement errors
  • Different in growth rate between individuals
  • Fetal sex
  • Maternal conditions
  • CRL may indicates an early IUGR.

Tend to underestimate GA by 2-3days

After 12wa CRL m inaccuracy of 7-10days

crown rump length1
Crown – rump length
  • To establish correct GA :


Longitudinal section

The end point of the crown & rump clearly defined

Placing the calipers correctly on this defined end point.

crown rump length2
Crown rump length
  • CRL between 5-7ws are incorrect:
  • The very early embryo is unflexed.
  • The full length of the embryo has not been obtained.
  • The end point of the embryo is closely adjacent to yolk sac or wall of GS.
crown rump length3
Crown rump length
  • After 7ws its easily to identify the end points of the embryo, but insure that you are imaging the maximum length of the embryo.
  • The CRL should be measured from 3 different images and the measurements should be agree to within 3mm in the embryo & 5mm in the fetus.
crl measurement problems
CRL measurement problems
  • Any degree of flexion of fetal spine will produce an underestimate of CRL when linear calipers are used.
crl measurement problems1
CRL measurement problems
  • When the fetus remains obstinately curled, you have 4 choices:
  • Sit and wait.
  • Measure the flexed length using onscreen nonlinear measuring facilities.
  • Use the linear caliper to measure the parts of the fetal length that are in straight sections and add them together.

4-Using a linear calipers along the flexed length.

This is not to be recommended under any circumstances

How easy to produce errors of 10-15mm simply by

measuring 12-13ws fetus incorrectly


2nd trimester biometry-

–assessing gestational age

2nd trimester biometry assessing gestational age
2nd trimester biometry –assessing gestational age
  • BPD & FL provide the most accurate assessment of GA.
  • HC, TCD & AC they provide further confirmation of GA and aid in the exclusion of growth related abnormalities.
  • The BPD has traditionally been the most widely used ultrasound parameter in the estimation of gestational age
  • - A single optimal measurement of the BPD will predict the gestational age to within ± 5 days.
biparietal diameter bpd
Biparietal diameter (BPD)
  • BPD : maximum diameter of transverse section of the fetal skull at the level of parietal eminence .
  • BPD, OFD & HC can be measured from:

Lateral ventricles view

Thalami view

lateral ventricles view of bpd
Lateral ventricles view of BPD
  • A rugby- football- shaped skull, rounded at the back (occiput) and more pointed at the front (synciput).
  • Long midline equidistant from the proximal and distal skull.
lateral ventricles view of bpd1
Lateral ventricles view of BPD
  • The CSP bisecting the midline 1/3 of the distance from the synciput to the occiput.
  • The two ant horn of lateral ventricles placed about the midline.
  • The two post horn of lateral ventricles placed about the midline
trans thalamic view of bpd
Trans thalamic view of BPD

A rugby- football- shaped skull, rounded at the back (occiput) and more pointed at the front (synciput).

Short midline equidistant from the proximal and distal skull

trans thalamic view of bpd1
Trans thalamic view of BPD
  • The CSP bisecting the midline 1/3 of the distance from the synciput to the occiput.
  • The thalami
  • The basal cisterns.



  • Outer to outer!!!!!
  • Outer to inner!!!!!!!
trans cerebellar diameter1
Trans cerebellar diameter

It’s a beast dater of pregnancy.

TCD in mm= ws of gestation

until 22ws.


Suboccipitobregmatic view

  • M. at 90 degree with the longest axis
  • The bonus with TCD is that it force the operator to image the entire post fossa which indirectly refractor of the integrity of neural tube.
  • The same plane of nuchal fold thickness.
measurement of hc
Measurement of HC
  • Short midline, 90 degrees to the beam
  • Oval shape
  • Thalami
  • NO cerebellum or orbits
  • Cavum septum pellucidi
  • Measure circumference of outer bone (usual to put calipers at occiput then sinciput)
abdominal circumference
Abdominal circumference
  • The AC is measured in a location that estimates liver size.
  • The liver is the largest organ in the fetal torso, and its size reflects aberrations of growth, both growth restriction and macrosomia.

A circular section of the abdomen ,unbroken & short rib echo of = size on each side.

  • A cross-section of one vertebra visualized as a triangle of 3 white spots.
  • A short length of umbilical vein (1/3 from ant abd wall to spine).
  • The stomach in the left side of the abd.
  • NO kidney, bladder, heart. Adrenal allowed

A. This plane is too caudal

B. This is the correct level for AC.

C. this plane is too inclined in a craniocaudal axis.

femur length
Femur length
  • 12ws to term, The upper femur , Full length of femur
  • Soft tissue should be visible beyond both ends of the femur.
  • The bone should not appear to emerge with the skin of the thigh at any point.
femur length1
Femur length
  • The FL measurement is made from the center of the U shape at each end of the bone.
  • Good practice, to obtain measurements from separate image of the same femur. (1mmof each other).

Cephalic index= BPD/OFD=80± 5

Dolichocephaly ( narrow BPD) ,75

Brachycephaly (wide BPD)

2 nd trimester fetal anatomy
2nd trimester fetal anatomy
  • Intracranial anatomy.
  • Nuchal area.
  • Fetal spine
  • Fetal chest & diaphragm.
  • Fetal heart
  • Fetal abdomen
  • Urinary tract.
  • Fetal limbs
  • Fetal face.
  • Fetal sex
intracranial anatomy
Intracranial anatomy
  • Cerebral ventricles
  • Thalami & 3rd ventricle
  • Cerebellum
  • Cisterna magna
choroid plexus cyst
Choroid plexus cyst
  • <10mm in diameter.
  • Unilateral or bilateral.
  • Resolve by 26ws
  • 0.5-2%

Cisterna magna

fetal spine
Fetal spine

Lumbar spine, transverse axial sonogram, 23 weeks. Well-defined ossification of the laminae (L). C, centrum; arrows, neurocentralsynchondroses.

fetal abdomen
Fetal abdomen
  • Anterior abdominal wall &Cord insertion
  • Major blood vessels
  • Gall bladder
  • Spleen
  • bowel
anterior abdominal wall
Anterior abdominal wall
  • The integrity of the ant abdominal wall has to be checked; using the transverse abdominal section.The insertion of the cord and confirmation of the presence of 3 vessels should be done.
  • Its important as well to visualized the fetal bladder in the pelvis to exclude extrophy.
gastrointestinal tract
Gastrointestinal tract
  • The fetal stomach is visible from 9ws inwards as sonolucent cystic structure in the upper left quadrant of the abdomen.
  • The liver occupies most of the upper abdomen.

Observe the fetal abdomen in both cross & longitudinal section to exclude evidence of obstruction or area of increased echogenicity:

Echogenic bowel

Echogenic foci of the liver

the kidneys urinary tract
The kidneys & urinary tract
  • The kidneys & adrenals, located below the level of the stomach, on either side and anterior to the spine.
  • They are visible from 9ws to 12ws.
the kidneys urinary tract1
The kidneys & urinary tract
  • Its important to assess the size and texture of the kidneys
  • The average kidneys circumference (of the two together) should be about one third of the abdominal circumference through the pregnancy.
  • They appear slightly hypoechoic when compared with liver .
  • The texture should be mildly heterogeneously echogenic
the kidneys urinary tract2
The kidneys & urinary tract
  • The fetus empties its bladder every 30-45min
  • Renal pelvis Ap. diameter :
  • 5mm in the 2nd trimester
  • 10mmin the 2nd trimester
fetal limbs
Fetal limbs
  • The four limbs of the fetus must be visualized.
  • This should includes visualization of:
  • long bones: femur, tibia, fibula, humerus, radius & ulna.
  • Hands &feet.
  • Shape & echogenicity .
  • Relation of the feet to the legs.
relation of the feet to the legs
Relation of the feet to the legs.
  • When tibia & fibula in longtudenal section only a cross section of the talus should be seen.

When the planter or foot print obtained with the same section with tibia & tibia talipes should be suspected.

  • A planter view of the foot to exclude polydactyl or syndectyly.
  • Look at the position of the big toe relative to the 2nd to exclude a sandal gap.
fetal sex
Fetal sex
  • Its possible to determine the sex of the fetus trans abdominally from 14ws but its frequently difficult to make a definitive diagnosis until 16ws.
  • Never guess ; if you are insure, say you do not know.