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2011-12-03 22:42:54

The normal first trimester
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  1. chorionic villi sampling (CVS)
    biopsy of chorion frondosum through abd wall or by way of vagina and cervix at 10-13 weeks of gestation to obtain fetal cells for prenatal diagnosis of chromosomal abnormalities
  2. conceptual age or
    embryologic age
    conception at the first day of pregnancy

    subtract 2 weeks from gestational age
  3. Gestational age or
    menstural age
    • used by physicians and sonographers
    • first day of the last menstural period as the beginning of gestation

    add 2 weeks to on to conceptual age
  4. fetus
    after the first 10 weeks
  5. embryotroph
    fisrt 12 days after conception during implantation

    implantation- blastocyst (7-9 days)
  6. Embryo
    from implantation until the 10th wk menstural age (8th embryologic)

    at 10 weeks it has everything it will ever have
  7. fertilization time line
    ovum released on day 14 of cycle in distal 1/2 of fallopian tube, fertilization 1-2 days later

    corus luteum secretes progest and estrogen

    zygote divides to 16 cell morula then blastocyst

    blastocyst contains trophoblastic cells in inner cell mass forms embryo

    trophoblastic cell secrete hcg- maternal preg response
  8. hCG
    human chorionic gonadotrophin

    causes endometrium to convert to dicidua(glycogen rich mucosa)
  9. lacunae
    trophoblasts eat into decidua to create "blood pools" that form as maternal cappillaries erode to nourish the proliferating trophoblastic cells
  10. Placenta
    made from lacunae and trophoblastic cells that develop into circulation complex that will sustain pregnancy
  11. implantation
    when complete the trophoblast formed primary villi which encircle early gest. sac

    inner cell mass matures into bilaminar embryonic disk, future embryo, and primary yolk sac
  12. primary yolk sac
    23 days- pinched off by extra embryonic coelom and forms secondary yolk sac

    • not seen sonographically
    • looks anechoic at 5 weeks
  13. secondary yolk sac
    seen sonographically through 1st trimester starting at 5.5 weeks, not seen after 12 weeks

    btwn chorion and amnion

    should not exceed 6mm

    • 1. nutrients to developing embryo
    • 2. hematopoiesis
    • 3. develop endoderm (primative gut)

    • should be seen with MSD 10-15mm
    • must be seen with MSD 20mm
  14. embryonic phase (period)
    • weeks 4-10
    • all major internal and external structure develop

    • initial heart beat 5.5-6 weeks
    • turns to C shape
  15. CRL
    • crown-rump legnth, (1975)
    • use as early as 5.5 wks tv
    • measures 35mm by end of 10th week
    • use up to 12 weeks
    • most accurate way to age baby +/- 4-5days
  16. Fetal period
    • begins last two weeks of 1st trimester (11-12)
    • head is 1/2 of CRL
  17. Gestational sac size and hCG levels
    • increse proportionally until 10th menstural week
    • sac approx 45mm
    • sac can be seen transabd when hCG is 1800+ mIU/ml
  18. MSD
    • mean sac diameter
    • remains accurate through first 8wks
    • MSD=L(mm)+W(mm)+H(mm)/3
    • MSD(mm)+30=Menstrual age (days)
  19. normal IUP hCG
    level doubles every 3.5 days at less than 7 wks

    if not, could be ectopic

    • hCG plateau at 9-10 wks and decline
    • trisomy21- levels fall slower
  20. PAPP-A
    • Pregnancy-associated plasma protien-A
    • insulin like growth factor produced by trophoblastic (placental) cells
    • involved in bone and tissue formation
    • increses in advancing gest, low in trisomy 21 (9-11wks)
  21. 1st trimester protocol
    • presence of sac
    • mesurement of sac/embryo
    • presence of cardiac activity
    • fetal number
    • uterus, adnexa, cul-de-sac
  22. IUP can be seen...
    5th week of development measuring 1-2mm with an echogenic ring with solonlucent center (chorionic cavity)
  23. dicidua basalis
    myometrial or burrowing side of conceptus
  24. decidua capsularis
    villi covering of developing embryo
  25. double decidual sac sign
    interface btw decidua capsularis and echogenic vascularized decidua on opposite wall of the endometrial cavity

    sign of early IU gestation
  26. 1. yolk sac should be seen...
    2. embryo should be seen...
    • 1. when MSD is >12mm
    • 2. when MSD is >18mm

    Grows at rate of 1mm per day
  27. 1. secondary yolk sac seen...
    2. hear rate...
    3. amniotic cavity, chorionic cavity, yolk sac, and embryo
    • 1. 5-5.5 weeks
    • 2. 5.5 weeks
    • 3. 5.5-6 weeks
  28. Embryo
    • 5 weeks, CRL 3 mm
    • heart rate at 5.5 weeks (CRL >4mm)
    • btwn secondary yolk sac and immediate gest sac wall
    • as amniotic sac grows embryo and yolk sac become further apart
  29. Chorionic Cavity vs. amniotic cavity
    chor. surrounds the amniotic sac, yolk sac is btw the chorion and amnion

    both seen after 5.5 weeks

    chor. increased gain shows low level echos (increased density vs. amniotic)

    chor. initial dumping ground for waste until placenta takes over

    amniotic cav. expands and chorionic decreases

    fusion of both (chorioamniotic fusion) at 14-15wks
  30. Amnion
    smooth membrane enclosing fetus and amniotic fluid, loosly fused with outter chorionic membrane except at placental insertion of umbilical cord, where amnion is continuous with membrane surrounding umbilical cord
  31. amniotic fluid
    produced by umbilical cord, and membranes the fetal lung, skin, and kidneys
  32. C-shaped embryo
    6th week from trilaminar embryonic disk
  33. yolk stalk
    umbilical duct connecting yolk sac with embryo

    incorperated into embryo developing foregut, midgut, hindgut, and GI tract, biliary, liver, pancreas
  34. umbilical cord
    connecting lifeline btwn fetus and placenta, 2 umbilical arteries and one vein, encased in whartons jelly
  35. embryonic cranuim and spine
    6wks- spine from ectoderm- evolved from primitive neural tube-closes and can be visualized- fetal pole

    • 7wks- cranial neurofoldsand closure of neuropore complete
    • 7wks- brain- single fluid filled vesicle

    • 8th wk- brain- three vessicles
    • 1. prosencephalon
    • 2. mesencephalon
    • 3. rhombencephalon
    • a. cephalic- mentencephalon
    • b. caudal- myeloencephelon

    9wks- echogenic choroid plexus

    10wks- cerebellum, medulla, med. oblongota
  36. limb development
    • 6th week- limb buds recongizable (tadpole)
    • upperlimbs 1st lower 2nd
    • hands and feet- fingers/toes by 10th wk
    • calcification of bones at 10wk- easier to see
  37. skeletal ossification
    • 8wks- calcification of clavicle
    • 9wks- frontal cranial bones, mandible
    • 10th- bony palate
  38. physiologic herniation of bowel
    • 6 wks- abd wall
    • midgut- small bowel, cecum, asc colon, trn colon
    • midgut herniates into base of umb cord
    • 11wks descends into fetal abd
  39. embryonic heart
    • first functional organ
    • starts beating at 35 days (5-5.5 wks)
    • 8th wk- adult heart configuration
    • always seen at 46 mens days, CRL >4mm
    • 6wk- 90-115 bpm
    • 9wk- 140-160 bpm
  40. Gestation age
    two parameters used: CRL and gestational sac size
  41. amniocentesis
    trandabd removal of amn fluid from amn cavity using us, studies of fluid determine fetal karyotype, lung maturity, and rh condition

    performed at 16 wks
  42. nuchal translucency measurement
    nuchal translucency (NT)- small amt fluid along back

    risk assessment test

    differences in nt btwn twins may be sign of twin to twin transfusion syndrome
  43. nasal bone
    absence of nasal bone associated with trisomy 21 in late 1st trimester
  44. tricuspid regurgitation (TR)
    • increased risk of aneuploidy
    • requires doppl of small fetus= only if necessary, high risk
  45. multiple gestations
    diagnosed btwn 5.5-6 wks
  46. dizygotic twins
    • 70% all twins
    • dichorionic and diamniotic
  47. monochorionic/monoamniotic
    • crucial diagnosis
    • 50% mortality
  48. monochorionic/diamniotic
    twins in same gest sac/chorion, 2 amnions, 2 yolk sacs, 2 embryos
  49. when can fetus survive outside
    • 25 weeks- many complications
    • 32 weeks- high survival- some complications
  50. anacephalic
    • no head
    • #1 neurotube defect