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Fetal biometry

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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Fetal biometry

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  1. Fetal biometry

  2. The common tomograms used : • Axial • Coronal • Sagittal (midline)

  3. 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

  4. 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.

  5. 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

  6. The differ US parameters used to estimate GA

  7. 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.

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

  9. Crown – rump length • To establish correct GA : Unflexed Longitudinal section The end point of the crown & rump clearly defined Placing the calipers correctly on this defined end point.

  10. 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.

  11. 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.

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

  13. 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.

  14. 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

  15. 2nd trimester biometry- –assessing gestational age

  16. 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.

  17. BPD • 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.

  18. 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

  19. 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.

  20. 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

  21. Lateral ventricles view of BPD

  22. 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

  23. 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.

  24. a b

  25. Measurement • Outer to outer!!!!! • Outer to inner!!!!!!!

  26. Trans cerebellar diameter

  27. Trans cerebellar diameter It’s a beast dater of pregnancy. TCD in mm= ws of gestation until 22ws.

  28. 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.

  29. 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)

  30. 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.

  31. 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

  32. A. This plane is too caudal B. This is the correct level for AC. C. this plane is too inclined in a craniocaudal axis.

  33. 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.

  34. 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).

  35. Confirming or assigning GA

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

  37. Cephalic index= BPD/OFD=80± 5 Dolichocephaly ( narrow BPD) ,75 Brachycephaly (wide BPD)

  38. Fetal anatomy survey

  39. 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

  40. Intracranial anatomy • Cerebral ventricles • Thalami & 3rd ventricle • Cerebellum • Cisterna magna

  41. Choroid plexus cyst • <10mm in diameter. • Unilateral or bilateral. • Resolve by 26ws • 0.5-2%

  42. Cerebellum Cisterna magna

  43. Nuchal area

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