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PREGNANCY 3 rd Trimester

PREGNANCY 3 rd Trimester. PREGNANCY 3 rd Trimester I. Uterine Changes A. Uterus experiences greatest period of growth B. Reaches into epigastric region by 8 th month C. Endometrium 1. Layer thickens 2. Glands enlarge, may penetrate myometrium.

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PREGNANCY 3 rd Trimester

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  1. PREGNANCY 3rd Trimester

  2. PREGNANCY 3rd Trimester I. Uterine Changes A. Uterus experiences greatest period of growth B. Reaches into epigastric region by 8th month C. Endometrium 1. Layer thickens 2. Glands enlarge, may penetrate myometrium

  3. PREGNANCY 3rd Trimester, con’t… • Location of uterine fundus by developmental week

  4. Uterine changes, continued … D. Myometrium: arranged into three distinct layers 1. External layer: beneath peritoneum a. Fibers pass transversely across fundus b. converge @ superior angles of uterus

  5. Uterine changes, continued … c. Fibers extend onto 1. fallopian tubes 2. round ligaments 3. ovarian ligaments 2. Middle layer: a. thickest b. meshwork of random fibers c. many blood vessels

  6. Uterine changes, continued … Myometrium • Inner layer: • fibers arranged circularly • form cones • 1. Apices surround fallopian tubes • 2. Fibers form sphincters around internal ossa of tubes

  7. Uterine changes, continued … Myometrium • Smooth muscle fibers hypertrophy a. >800% (8x) larger • muscle fibers undergo mitosis 1. only during pregnancy 2. Lose fibers post-partum

  8. Uterine changes, continued … • Wall of uterus thins as pregnancy progresses • Placental “ascension” or “migration” 1. During the last part of the 3rd trimester 2. Differential growth of lower uterine segment 3. Artifact of development

  9. PREGNANCY 3rd Trimester, con’t… • Early fetal period • 8-16 weeks • Middle fetal period • 17-30 weeks • Late fetal period • 13-38 weeks

  10. PREGNANCY 3rd Trimester, con’t… • II. Placental Changes • A. Chorionic Plate • 1. Strong interface visible • 2. Between amniotic cavity and fetal surface of placenta • 3. After 12th menstrual week = Grade 0, mature placenta • 4. Placenta attains a diffuse echogenic pattern

  11. PREGNANCY 3rd Trimester, con’t… • Normal Mature Placenta • Maternal side • Fetal side • Microscopic view

  12. Placental Changes, con’t…. • B. Early in 3rd trimester • 1. changes occur • 2. Detectable sonographically • 3. Grade I changes: • a. first noted @ 30-32 weeks b. Placenta is 3.8 cm

  13. Placental Changes, continued … d. Chorionic plate develops “wavy” appearance e. Homogeneous look is lost f. See increased glands, calcifications g. see more scattered echogenic regions

  14. Placental Changes, continued … • 2. Grade II changes • a. 34-36 weeks • b. Chorionic plate develops marked indentations

  15. Placental changes, continued… c. Comma-shaped septa extend from chorionic plate toward basalis d. Placenta becomes more echogenic e. Placental “mottling” appears

  16. Placental Changes, continued … • 3. Grade III changes: a. 38-40 weeks (3.5 cm) • b. Septa extend thru placenta • c. To decidua basalis • d. Divide placenta into “cotyledons” • e. Calcium deposits create echoes

  17. Placental changes, continued … • f. May find “cysts” between chorionic plate and placenta • g. Areas of excessive fibrin deposition • h. placenta starts deteriorating • i. Venous lakes develop

  18. Placental changes, continued … • C. Thickness gradually decreases after 32 weeks • D. Growth ceases after 38 weeks • E. Changes normal for senescent placenta • 1. At birth: weighs ~ 1 lb • 2. Size: ~6-8” diameter • 3. Surface area: ~ 16 m2

  19. Pregnancy, 3rd Trimester, con’t… • Amount of amniotic fluid 1. Increases during pregnancy 2. May reach one gallon in late 3rd trimester

  20. PREGNANCY 3rd Trimester, con’t… • Placental variations • Succenturiate placenta • Circumvallate placenta • Battledore placenta • Velamentous placenta • May result in vasa previa

  21. PREGNANCY 3rd Trimester, con’t… • Fetal Structures • A. Fetal Head • 1. First visualized at 5-6 weeks • 2. After 12 weeks, details can be seen: • a. Falx cerebri • b. Ventricles • c. Thalami • d. Corpus callosum

  22. Fetal Structures: Fetal head • Septum pellucidum • Lateral fissure • Midbrain • Basilar artery i. Cerebral hemisphere j. cerebellum 8.0 mm 6 months 10.5 mm 9 months

  23. PREGNANCY 3rd Trimester, con’t… • Fetal Thorax • 1. Heart: evaluation after 10-12 weeks • a. Four chambers: “4 chambers @ 4 months” • b. Ventricular diameter: 34-41 weeks • c. Aorta: early on with Doppler Endocardial Cushion: green

  24. Fetal Thorax, Con’t… 2. Lungs: a. no clear boundaries between lungs, diaphragm, and liver b. unless fluid intervenes 3. Diaphragm: usually visible

  25. Fetal structures, continued … • Abdomen • 1. Stomach • a. upper left quadrant • b. by 12-15 weeks • 2. Fluid in small intestine by 2nd trimester • 3. Descending colon • a. seen in late 3rd trimester b. filled with fluid and meconium G.I. Tract development at 3-4 months

  26. Fetal structures, Abdomen, cont… • 4. Umbilcal vein • a. visible in area of umbilicus • b. coursing superior and posterior to portal sinus (vein) • 5. Liver: • a. in upper right quadrant • b. with hepatic & portal veins • c. largest organ by 8 weeks

  27. Fetal structures, continued … • Pelvis & retroperitoneum • 1. Kidneys: seen @ 15-20 weeks • 2. Urinary Bladder: • a. seen @ 13-15 weeks • b. in 3rd trimester, urine-filled 6 weeks 7 weeks 9 weeks

  28. Fetal structures, continued … • Other structures • 1. Skeletal components • a. Axial skeleton • b. Long bones • 2. Extremities • 3. Genitalia by 10 weeks (+/-)

  29. IV. FETAL CIRCULATION • A. General • 1. Ovum and yolk sac provide initial nutrients to embryo • 2. Other means must develop early on

  30. FETAL CIRCULATION, CON’T… 3. Blood vessel and blood formation a. begin15-16 days after fertilization b. in mesoderm of yolk sac, body stalk, chorion 4. Cardiovascular system first to develop

  31. Fetal circulation, continued … • 5. Blood flow begins end of the third week • 6. Heart beat begins about 22 days • 7. REMEMBER: • a. fetus is totally dependent on outside source for oxygen, nutrients, and waste disposal. • b. This source is the placenta

  32. Fetal circulation, continued … • Course of blood through fetal circulation • 1. Always begin at placenta 2. Vessels named with respect to fetus 3. Blood leaves placenta via umbilical or placental vein(+ O2 blood)

  33. Fetal circulation, continued … • 4. Travels in umbilical cord • a. Through umbilicus • b. Into baby’s body • 5. Ascends along falciform ligament • a. To inferior surface of liver • b. Here, enters liver

  34. Fetal Circulation Umbilical Vein

  35. Fetal circulation, continued … • 6. At porta hepatis, umbilical vein divides: • a. Portal vein: carries blood through liver  hepatic veins  IVC • b. Ductus venosus: goes directly to IVC

  36. Fetal Circulation Ductus Venosus Portal Vein

  37. Fetal Circulation, continued … • Blood in IVC is –O2 blood, and is • mixes with +O2 blood from hepatic veins, ductus venosus • is now “mixed” blood • IVC enters right atrium

  38. Fetal Circulation IVC

  39. Fetal Circulation, continued … • some blood follows post-partum path b. Most blood is diverted • 1. by valve of IVC (Eustachian valve) • 2. through foramen ovale into left atrium

  40. Fetal Circulation, con’t… • Foramen Ovale • Eustachian Valve

  41. Fetal Circulation, continued … • 9. From left atrium: • blood is pumped to left ventricle • out the aorta • throughout systemic circulation

  42. Fetal Circulation, continued … • Blood from head and upper extremities a. returns to right atrium via SVC b. mixes with blood from IVC 11. Blood to lower body a. passes from aorta common iliac arteries internal iliac arteries

  43. Fetal Circulation SVC IVC Common Iliac Arteries Umbilical Arteries

  44. Fetal Circulation, continued … • 12. Fetal lungs are non-functional • a. require minimal blood supply • b. shunt is present between pulmonary artery and aorta • c. ductus arteriosus: by-passes lungs

  45. Fetal Circulation, con’t… Ductus Arteriosus

  46. Fetal Circulation, continued 13. Vessels in umbilical cord a. single large vein b. two smaller arteries

  47. Fetal circulation, continued … • Recap of fetal circulation: • a. Oxygenated blood carried by • 1. umbilical vein • 2. portal vein • 3. ductus venosus

  48. Fetal circulation, continued … • b. Placenta is: • 1. Fetal organ of respiration, nutrition & excretion • 2. Most blood from placenta a. goes thru liver b. before entering IVC

  49. Fetal circulation, continued … • Eustachian Valve 1. directs most blood from IVC to left atrium 2. directs blood from SVC to right ventricle

  50. Fetal circulation, continued … • d. Blood from umbilical vein, IVC 1. go from L.A. to L.V. to aorta • 2. then mostly to head, upper extremities • e. Descending aorta contains mixed blood

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