Obstetrical Measurements 2 nd & 3 rd Trimester

1. Obstetrical Measurements2nd & 3rd Trimester Fetal Biometry Workshop Day 2 & Day 3

2. Learning Objectives • List guidelines for 2nd & 3rd trimester OB exams • Evaluate fetal anatomy

3. Protocol – 2nd & 3rd Trimester • BPD & HC • Cerebellum • Cisterna Magna • Choroids • Lateral Ventricle • Diaphragm • AC • Bladder • Kidneys • Fetal Heart • 4 chamber • LV & RV outflow • 3 Vessel view • Femur length • Extremities • Phalanges • Gender • Spine • Cervix • Fetal Lie • Situs • AFI • Placenta • Cord • Facial Profile • Nose & Lips

4. Cervix • Avoid measuring the cervix with a LUS contraction or overly distended bladder. • Need fluid in front of the internal cervical os to comment on relationship to placenta

5. Cervix • Normal = 3-4cm • If >4 bladder is probably too full • Empty and rescan • If < 3cm • Evaluate with translabial first then transvaginal • If evaluating by TV, maternal bladder should be emptied • Watch out for curved cervix make sure you trace the curve instead of straight line

6. Cervix • Preterm labor • <37 weeks gestation • Cervical effacement and dilatation • Funneling • Cervix is shortened • The cervix appear to be separating apart

7. Why we need to see cervix…

8. Fetal Lie

9. Fetal Lie • Cephalic/Vertex • Right side • Fetal spine toward maternal Right • Stomach towards maternal front • Left Side • Fetal spine toward maternal left • Stomach towards maternal back • Breech • Right Side • Fetal Spine Toward maternal left • Stomach towards maternal front • Left Side • Fetal spine toward maternal Right • Stomach towards maternal back • Transverse

10. Fetal Lie

11. Fetal Lie

12. Breech Position • Complete • Baby sits with legs crossed • Frank • Bottom first • Legs are up by face • Footling • Either foot comes first

13. Vertex or Breech?

14. Vertex or Breech?

15. Vertex or Breech?

16. Situs • Situs Solitus • Larger lobe liver on right • Gallbladder on right • Stomach on left • Spleen posterior lateral • Abdominal aorta posterior • IVC anteriorly on right • Situs Inversus • Right / left relationships reversed • Heterotaxy or Situs ambiguous • Complex / hard to define • Jumbled-up arrangement non paired organs • Asplenia or Polysplenia

17. Amniotic Fluid • Aides in symmetrical growth • Cushions fetus • Prevents adhesions • Freedom of movement for fetus • Aides in lung, GI, and musculoskeletal development • Maintains constant temp. for fetus • Prevents infection

18. Production of AF • 1st Trimester • Cells lining amnion secrete AF • H2O diffuses across chorion frondosum • Prior to kidney function, passive diffusion from fetus across skin • Amnion covers cord • 12 wks to term • 12-15 weeks kidneys start to produce amniotic fluid • Fetal kidneys produce majority of fluid through urination • AF increases till about 30 weeks

19. Resorbtion of AF • Ingested by fetus • At term rate of ingestion = urine production • Equilibrium must be maintained

20. Composition of AF • Early pregnancy is clear or translucent fluid • Later in pregnancy it becomes cloudy • Vernix • Cells from skin and cord • Lanugo (fetal body hair) • Alkaline pH • 98% H2O/2% is salts and organics

21. Not measured till 18 wks Make sure transducer is perpendicular, No tilting of transducer Use Color to make sure no cord or baby part in pocket Cord can be difficult to see especially in 3rd trimester pregnancies Measure A-P Measuring AF

24. Placenta

25. Placenta

26. Umbilical Cord • 3 vessel cord = 2 arteries + 1 vein • Oxygenated blood through vein • Deoxygenated blood through arteries • Transverse slice through cord, Mickey mouse • Want to see cord insertion site (fetus and placenta)

27. Umbilical Cord

28. Cord Insertion

29. Facial Profile • Are the orbits normally spaced? • Are the nose and nasal bridge clearly imaged? • Is a proboscis or cebocephaly present? • Are any periorbital masses? • Is the upper lip intact? • Is the tongue normal size? • Is the chin abnormally small? • Are the ears normal size and position?

30. Nose & Lips

31. Fetal Neural Axis

32. BPD & HC • Thalami are paired • Lie on both sides of 3rd ventricle • CSP • Sit between frontal horns of the lateral ventricles

33. Ventricles

35. Ventricles

36. Cerebellum

37. Cerebellum

38. Cisterna Magna • Fluid filled structure • Lies between the cerebellum and occipital bone • > 10 mm - Relate to Dandy-Walker malformation

40. Fetal heart views • 4 chamber view • 5 chamber view • Short axis sweep

41. The aorta and pulmonary artery should appear about equal in size. PA AAo Ductus Arteriosis SVC DAo

42. Fetal Diaphragm • Visualization • 3% @ 14 weeks • 43% @ 20 weeks • 81% @ 35 weeks

43. Biometry in Abdomen • Abdominal circumference • At level of umbilical cord • Outer perimeter of abdomen

44. Fetal Bladder & Kidneys • Begin to develop ~ 5th week • Function & produce urine ~ 11 weeks • Visible at 17 to 22 weeks - 3rd trimester easier to image due to perirenal fat

45. Spine ~ 16 weeks • Normal neural arch - a closed circle with an intact skin covering • Spina bifida the arch is "U" shaped and there is an associated bulging meningocele (thin-walled cyst) or myelomeningocoele.

46. Normal Fetal Limbs

47. Shaft fairly straight, symmetric and evenly ossified Lateral surface straight & Medial curved Accurate only when the image shows two blunted ends Femur Length

48. Female Genitalia • Hamburger

49. Male genitalia • Turtle sign • If you think cord put on color Doppler

50. Nuchal Translucency Screening Amnion Nicolaides and colleagues, 1992