Fetal biometry

Fetal biometry

The common tomograms used :AxialCoronalSagittal (midline)

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 longIrregularTaking COCWomen had bleed in early pregnancyLactating women

Fetal biometry

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 diameterGestational sac volumeCrown rump lengthBiparietal diameterFemur length

Mean GC diameter4-6wsGS volume4-6wsCrown rump length6-12wsDefer measurement12-15wsBPD, FL, AC15-24wsGA cannot accurately determined by US24ws inwardThe differ US parameters used to estimate GA

Crown rump lengthThe 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 errorsDifferent in growth rate between individualsFetal sexMaternal conditionsCRL may indicates an early IUGR.

Tend to underestimate GA by 2-3daysAfter 12wa CRL m inaccuracy of 7-10days

To establish correct GA :UnflexedLongitudinal sectionThe end point of the crown & rump clearly definedPlacing the calipers correctly on this defined end point.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 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.Crown rump length

Any degree of flexion of fetal spine will produce an underestimate of CRL when linear calipers are used.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.CRL measurement problems

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 incorrectly2nd trimester biometry- assessing gestational ageBPD & 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.2nd trimester biometry assessing gestational ageThe 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.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 viewThalami view

Biparietal diameter (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 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

Lateral ventricles view of BPD

Lateral ventricles 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 skullThe CSP bisecting the midline 1/3 of the distance from the synciput to the occiput.The thalamiThe basal cisterns.

Trans thalamic view of BPD

abMeasurement

Outer to outer!!!!!Outer to inner!!!!!!!

Trans cerebellar diameter

Trans cerebellar diameter

Its a beast dater of pregnancy.TCD in mm= ws of gestation until 22ws.Suboccipitobregmatic viewM. at 90 degree with the longest axisThe 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.

Short midline, 90 degrees to the beamOval shapeThalamiNO cerebellum or orbitsCavum septum pellucidiMeasure circumference of outer bone (usual to put calipers at occiput then sinciput)

Measurement of HC

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.Abdominal circumference

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. 12ws to term, The upper femur , Full length of femurSoft 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 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).

Femur length

Confirming or assigning GA

Assigning GA for the 1st time in the 2nd trimester

Dolichocephaly ( narrow BPD) ,75

Brachycephaly (wide BPD)Cephalic index= BPD/OFD=80 5

Fetal anatomy surveyIntracranial anatomy.Nuchal area.Fetal spineFetal chest & diaphragm.Fetal heartFetal abdomenUrinary tract.Fetal limbsFetal face.Fetal sex2nd trimester fetal anatomyCerebral ventriclesThalami & 3rd ventricleCerebellumCisterna magnaIntracranial anatomy