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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.

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Presentation on theme: "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."— Presentation transcript:

1 PREGNANCY 3 rd Trimester

2 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

3 PREGNANCY 3 rd 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. 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 3. Inner layer: a. fibers arranged circularly b. form cones 1. Apices surround fallopian tubes 2. Fibers form sphincters around internal ossa of tubes

7 Uterine changes, continued … Myometrium 4. Smooth muscle fibers hypertrophy a. >800% (8x) larger b. muscle fibers undergo mitosis 1. only during pregnancy 2. Lose fibers post-partum

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

9 PREGNANCY 3 rd Trimester, con’t… Early fetal period 8-16 weeks Middle fetal period weeks Late fetal period weeks

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

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

12 Placental Changes, con’t…. B. Early in 3 rd trimester 1. changes occur 2. Detectable sonographically 3. Grade I changes : a. first 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 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 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 m 2

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

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

21 III.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 PREGNANCY 3 rd Trimester, con’t…

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

23 PREGNANCY 3 rd Trimester, con’t… B.Fetal Thorax 1. Heart: evaluation after weeks a. Four chambers: “4 4 months” b. Ventricular diameter: 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 … C. Abdomen 1. Stomach a. upper left quadrant b. by weeks 2. Fluid in small intestine by 2 nd trimester 3. Descending colon a. seen in late 3 rd 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 … D. Pelvis & retroperitoneum 1. Kidneys: weeks 2. Urinary Bladder: a weeks b. in 3 rd trimester, urine-filled 6 weeks7 weeks9 weeks

28 Fetal structures, continued … E. 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 … B. 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 (+ O 2 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 … 7. Blood in IVC is –O 2 blood, and is a. mixes with +O 2 blood from hepatic veins, ductus venosus b. is now “mixed” blood 8. IVC enters right atrium

38 Fetal Circulation IVC

39 Fetal Circulation, continued … a. 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: a. blood is pumped to left ventricle b. out the aorta c. throughout systemic circulation

42 Fetal Circulation, continued … 10. 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 13. Vessels in umbilical cord a. single large vein b. two smaller arteries Fetal Circulation, continued

47 Fetal circulation, continued … 14. 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 … c. 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

51 Fetal Circulation Descending Aorta

52 Fetal circulation, con’t… C. Changes in Cardiovascular System at Birth 1. After pulmonary respiration begins a. the ductus arteriosus constricts b. blood flows to lungs

53 Fetal circulation, con’t… 2. More blood returns to left atrium a. flow thru foramen ovale stops b. Seals to become fossa ovalis 3. Ductus arteriosus a. fills with fibrous C.T. b. becomes ligamentum arteriosum

54 Fetal circulation, con’t… 4. Cutting umbilical cord causes vessels to collapse, seal a. Umbilical vein ligamentum teres hepatis b. Ductus venosus ligamentum venosum c. Proximal umbilical arteries internal iliac arteries d. Distal umbilical arteries lateral umbilical ligaments

55 Fetal Vessels: Postnatal Changes Ligamentum arteriosum Fossa ovalis Ligamentum venosum Ligamentum teres hepatis Lateral umbilical ligaments

56 Fetal circulation, con’t… Patent Urachus Urachal Cyst D. Urachus (median umbilical ligament) 1. Obliterated remains of allantois 2. Attaches urinary bladder to abdominal wall 3. Can form urachal cyst (rare)

57 Fetal circulation, con’t… 3. Passes superiorly from apex of bladder to umbilicus 4. Composed of fibrous C.T. and smooth muscle 5. Lies between umbilical ligaments

58 V. THIRD TRIMESTER BLEEDING A. Abruptio Placentae (Placental abruption): 1. Premature separation of a normally implanted placenta 2. May be mistaken for placenta previa 3. May be only a few mm separation or a complete detachment

59 Third trimester bleeding, con’t. 4. Retroplacental bleeding occurs 5. May be external or concealed 6. Signs and symptoms vary a. depends on degree of separation b. amount of blood loss

60 Third Trimester Bleeding, continued … B. Placenta Previa: 1. Placenta implants over internal os of cervix 2. Occurs in 1:200 cases 3. False positive rate of 10%

61 Placenta Previa Marginal Previa Partial Previa Complete Previa

62 Third Trimester Bleeding, continued … 4. Symptoms: a. sudden painless vaginal bleeding b. in late third trimester c. Followed by painless massive bright red bleeding

63 Third Trimester Bleeding, continued … 5. May be mistaken for abruptio placentae 6. Ultrasound is diagnostic modality

64 Third trimester bleeding, continued … C. Rh Incompatibility: [erythroblastosis fetalis, hemolytic disease of the newborn (HDN)] 1. lysis of fetal RBC’s 2. due to Rh - isoimunization 3. Rh - multiparous female 4. Rh + father and fetus

65 Third trimester bleeding, continued … 5. Leads to: a. hemolysis of fetal RBC’s b. anemia of fetus c. congestive heart failure d. may cause jaundice

66 Erythroblastosis Fetalis, continued … 3. Caused by transplacental transmission of maternal anti-Rh antibodies (Ab) a. All cells contain antigens on cell membranes, so…. b. All RBC’s contain antigens cell membranes

67 Erythroblastosis Fetalis, continued … c. ABO Antigens (Ag): 1. type A has A antigens 2. Type B has B antigens 3. type AB has both A & B 4. type O has neither Ag d. Rh: Rh + has antigen Rh - lacks antigen (ABO & Rh: major antigens involved in antibody incompatibility)

68 Erythroblastosis Fetalis, continued …. 4. At birth, baby’s blood may mix with mom’s (~40%) 5. Mom makes antibodies to Rh + 6. During succeeding pregnancies, antibodies cross placenta 7. Cause baby’s blood to agglutinate

69 Erythroblastosis Fetalis, continued … 9. Rhogam a. antibody formation may be prevented: “fools” mom’s immune system b. Rhogam given within 72 hours after fetus “leaves” c. Currently, Rhogam given to all Rh - moms every trimester

70 Twinning mechanisms and Placentation

71 Full-term Pregnancy


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