OB Shelf - anatomy and physiology of pregnancy

  1. Vulva
    blood supply
    • blood supply: external and internal pudendal arteries
    • lymph: Medial group of superficial inguinal nodes
    • nerve
    •  - anterior → ilioinguinal nerves, genital branch of genitofemoral nerves; 
    •  - posterior → perineal nerves and posterior cutaneous nerve of the thigh

  2. Vagina
    blood supply
    • Blood supply:
    • -Vaginal branch of uterin artery (primary)
    • -Middle rectal and inferior vaginal branches of hypogastric artery (internal iliac)

    • Nerve:
    • -Hypogastric plexus (sympathetic)
    • -Pelvic nerve (parasympathetic)
  3. Uterus
    anatomical components
    • Fundus: uppermost region of uterus
    • Corpus: body
    • Cornu: part that joins the fallopian tubes
    • Cervix: inferior part of cervix that connects vagina via cervical canal
    • Internal os: opening of the cervix on the uterine side
    • External os: opening of the cervix on the vaginal side
  4. Uterus
    • Mesometrium: visceral layer of peritoneum reflects against the uterus and forms this outmost layer
    • Myometrium: smooth muscle layer of uterus
    •      1. Outer longitudinal
    •      2. Middle oblique
    •      3. Inner longitudinal
    • Endometrium: Mucosal layer, columnar epithelium
  5. Uterus
    blood supply
    • Blood supply:
    • -Uterine arteries (from internal iliacs)
    • -Ovarian arteries

    • Nerve supply:
    • -Superior hypogastric plexus
    • -Inferior hypogastric plexus
    • -Common iliac nerves
  6. Broad ligament
    • Connection: lateral pelvic wall to the uterus and adenexa
    • Contains: fallopian tube, round ligament, uterine and ovarian blood vessels, lymph, utererovaginal nerves, ureters
  7. Round ligament
    • Connection: remains of gubernaculum; corpus of uterus down and laterally through the inguinal canal → labia majora
    • Contains: nothing
  8. Cardinal ligament
    • Connection: cervix and lateral vagina to the pelvic wall
    • Function: supports the uterus
  9. Fallopian (uterine) tubes
    Blood supply
    • Connection: extend from superior lateral uterus through superior fold of broad ligament to the ovaries
    • Blood supply: uterine and ovarian arteries
    • Nerve: Pelvic plexus (autonomic) and ovarian plexus)
  10. Fallopian tubes
    • Lateral to medial:
    • Infundibulum: the lateralmost part; free edge is connected to the fimbriae
    • Ampula: widest section
    • Isthmus: narrowest part
    • Intramural part: pierces uterine wall
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  12. Ovaries
    blood supply
    nerve supply
    • Location: posterior aspect of broad ligament; attached to the broad ligament by the mesoovarium. NOT covered by peritoneum
    • Blood supply: ovarian artery (from aorta at level L1); veins drain vena cava on the right, Left renal vein on the left
    • Nerve supply: Aortic plexus
    • Histology: covered by tunica albuginea (fibrous capsule); tunica albuginea is covered by germinal epithelium
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  14. Dating a pregnancy
    • Last menstrual period (LMP)
    • Ultrasound: progressively less accurate as GA increases. Should not be used past 20 weeks.
  15. Symptoms of pregnancy
    • Breast enlargement/tendernes (6 weeks GA)
    • Areolar enlargement and increased pigmentation (after 6 weeks GA)
    • Colostrum secretion (after 16 weeks GA)
    • Nausea with or w/o vomiting (from missed period)
    • Urinary frequency, nocturia, bladder irritability
  16. Chadwick's sign
    Bluish discoloration of vagina and cervix, due to congestion of pelvic vasculature in pregnancy
  17. beta human chorionic gonadotropin (β-hCG)
    site of production
    other uses
    • hCG (glycoprotein)
    • Production: syncytiotrophoblast cell s in developing placenta shortly after implantation

    Detection: 8-10 days after fertilization

    • Also elevated in:
    • -hydatidiform mole
    • -choriocarcinoma
    • -germ cell tumors
    • -Ectopically producing breast cancers and large cell carcinoma of the lung
  18. hCG levels during gestation
    • Levels should double every 48 hours in early pregnancy
    • 1 wk: 5-50mU/mL - assays detecting 25mU/mL recognize pregnancy with 95% sensitivity by 1 week post LMP
    • 2 wks: 50-500mU/mL
    • 3 wks: 100-10,000mU/mL
    • 4 wks: 1,000-30,000mU/mL
    • 5 wks: 3,500-115,000mU/mL
    • 6-8 wks: 12,000-270,000mU/mL
    • 8-12 wks: 15,000-220,000mU/mL
    • 20-40 wks: 3,000-15,000mU/mL
  19. urine hCG
    false positives
    false negatives
    • False positives:
    • -proteinuria
    • -Urinary tract infection

    • False negatives:
    • -too early
    • -urine is dilute
  20. plasma hCG
    • confirm urine hCG
    • Diagnosing ectopic pregnancy
    • Monitoring trophoblastic tumors
    • Screening for fetal abnormalities
  21. Fundal height
    • 12 wks: barely palpable
    • 15 wks: midpoint between pubic symphysis and umbilicus
    • 20 wks: at the umbilicus
    • 28 wks: 6 cm above the umbilicus
    • 32 wks: 6 cm below the xyphoid process
    • 36 wks: 2 cm below xyphoid process
    • 40 wks: 4 cm below xyphoid process
  22. Fetal heart tones
    earliest, and worrisome
    • Earliest: 8 weeks GA
    • Worrisome: not auscultated by 11 weeks' GA, should do an ultrasound
  23. Physiology in pregnancy
  24. Changes in pregnancy: Total body water
    • Increased by ~8.5 L
    • Composed of: fetal water, amniotic fluid, placental tissue, maternal tissue, edema, increased hydration of connective tissue, generalized swelling
  25. Changes in pregnancy: Energy requirement
    • Increased gradually from 10 weeks to 36 weeks by 50 to 100 kcal/day
    • Final 4 weeks, requirement increased by 300 kcal/day
  26. Changes in pregnancy: Weight gain
    • Ideal: 25 to 35 lbs during pregnancy
    • T1: 1.5 to 3 lbs
    • T2 and T3: 0.8 lbs/wk
    • Obese: should gain less that 25 lbs
  27. Changes in pregnancy: Metabolism
    • Overal increases in the second half of pregnancy
    • Carbohydrates: placenta is freely permeable to glucose
    • Insulin: increased in first half; insulin resistance in second half
    • Amino acids: plasma concentration of aa fall during pregnancy (hemodilution)
    • Lipids: all raised (most increase in triglycerides); cross the placenta
    • Fat: deposits in early pregnancy; primary source of energy in mid pregnancy
    • Cholesterol: increase turnover, all increased during pregnancy; raised in postpartum
    • Drugs: phenytoin falls during pregnancy; caffeine half-life is doubled; antibiotics are cleared more rapidly
  28. Screen for glucose intolerance/GDM
    • Screen at 26 to 28 weeks' GA
    • increased insulin in first half; insulin resistance in second half (physiologic)
  29. Changes in pregnancy: CNS
    psychiatric sx
    • Syncope:
    • -venous pooling in lower extremities
    • -dehydration
    • -hypoglycemia
    • -postprandial shunting of blood flow to the stomach
    • -overexertion during exercise

    • Psychiatric sx:
    • -Hormonal changes of pregnancy
    • -Progesterone → tiredness, dyspnea, depression
    • -Euphoria secondary to endogenous corticosteroids
  30. Changes in pregnancy: Respiratory
    Fetal PCO2 > maternal PCO2... must reset maternal respiratory center. Mechanism:

    • 1. Progesterone reduces the CO2 threshold at which respiratory center is stimulated and increases respiratory center sensitivity
    • →hyperventilation of pregnancy

    2. Tidal volume (TV) increases by 200ml

    3. Vital capacity (VC) increases by 100 to 200ml
  31. Changes in pregnancy: Cardiovascular
    • CO increases by 40% by week 10
    • -10% increase in stroke volume
    • -10 to 15% increase in pulse rate
    • -enlargement of heart and left ventricles
    • -heart is displaced anterolaterally secondary to rise in diaphragm (ECG changes can mimic ischemia)

    • Venous system: venous dilation
    • -relaxation of vascular smooth muscle
    • -pressure of enlarging uterus on IVC and iliac veins
  32. Changes in pregnancy: CV physical exam
    • After midpregnancy: 90% have S3
    • Systolic ejection murmurs: 96% of pregnant patients
    • Diastolic murmursnever normal
    • During labor: CO increases by 30% during each contraction (increase in stroke volume, not heart rate)
  33. Changes in pregnancy: Gastrointestinal
    Reflux esophagitis
    • Reflux esophagitis
    • -increased intragastric pressure
    • -progesterone causes a relative relaxation of esophageal sphincter

    Constipation: secondary to progesterone, which relaxes intestinal smooth muscle and slows peristalsis

    • Gallbladder:
    • -increased size
    • -empties slower
    • -Cholestasis, hormonal effects (?); also seen in some users of OCPs and hormone replacement therapy

    • Liver:
    • -hepatic function increases
    • -Plasma globulin and fibrinogen concentrations increase
    • -synthetic rate of albumin increases
    • -Velocity of blood flow in hepatic veins decreases
    • -Serum alkaline phosphatase increases largely due to placental production
  34. Changes in pregnancy: Genitourinary system
    • Urinary stasis: decreased peristalsis, mechanical compression
    • Asymptomatic bacteruria: 5 to 8% of pregnant women
    • Urinary frequency increases: bladder compression by uterus, fetal head descent
    • Nocturia: physiologic after T1 (up to 4 times per night)
    • Stress incontinence: relaxation of bladder supports
  35. Changes in pregnancy: Bladder
    • Bladder tone decreases
    • bladder capacity increases
  36. Changes in pregnancy: Ureters
    • Progressive dilatation and kinking in > 90% of women at >6 weeks
    • -Decreased urine flow rate
    • -dilatation is secondary to physical obstruction
    • -extends up to calyces → enlarged kidneys
  37. Changes in pregnancy: Renal function
    • RPF increases from T1: 30 to 50% above non-pregnant levels by 20 weeks; remains elevated until 30 weeks, then slowly declines
    • GFR: increases; 60% above nonpregnant levels by 16 weeks, remains elevated
  38. Changes in pregnancy: Renal tubule changes
    • Tubules lose some of their resorptive capacity: amino acids, uric acids, glucose are not as completely reabsorbed
    • Iincrease protein loss of up to 300mg/24hr
  39. Changes in pregnancy: Hematologic
    Plasma volume
    • Plasma volume: increased by 50% (hemodilution)
    • RBC: increases progressively during pregnancy (Ret count increases by >2%); MCV ususally increases
    • Hemoglobin: HbF concentration increases 1 to 2% during pregnancy
    • Erythrocyte Sedimentation Rate: rises in early pregnancy due to increase in fibrinogen
    • WBC: neutrophils increases in T1, rise until 30 weeks (number and activity/function); lymphocyte counts remains unchanged (function is suppressed)
    • Platelets: reactivity increased in T2 and T3, returns to normal post partum
  40. Changes in pregnancy: Endocrine system
    fetoplacental unit (hormones)
    • hCG (luteotropic): Co-regulates and stimulates adrenal and placental steroidogenesis; stimulates fetal tissue to secrete testosterone. Possesses thyrotrophic activity
    • hPL (human placental lactogen): anti-insulin and growth hormone-like effects (impaired maternal glucose and FFA release)
  41. Changes in pregnancy: Pituitary gland
    • Increases in weight and sensitivity
    • Prolactin: increases within a few days postconception; 10- to 20-fold higher at term
    • FSH: blunted response to GnRH; progressive decreased response
    • LH: response to GnRH diminishes and finally disappears
  42. Changes in pregnancy: Adrenal gland
    • Plasma cortisol/other corticosteroids increase progressively from 12 weeks to term; 3-5 times the normal levels
    • Half-life of plasma cortisol increases, clearance is reduced
  43. Changes in pregnancy: Thyroid gland
    • Thought to be due to excess estrogen in pregnancy:
    • -Increases in size
    • -T3/T4 and Thyroxine-binding globulin increase (mother should remain euthyroid)
  44. Changes in pregnancy: Parathyroid glands
    • PTH increases → increases maternal calcium absortpion (offset maternal loss to fetus)
    • At term, PTH levels are higher in the mother, but calcitonin is higher in the fetus
  45. Changes in pregnancy: Plasma proteins
    • Plasma protein concentrations fall by 20 weeks, mostly due to a fall in serum albumin
    • Reduced colloid osmotic pressure in plasma → edema in pregnancy
  46. Changes in pregnancy: Pancreas
    • Size of islets of Langerhans increases
    • Number of beta cells increases
    • Number of insulin receptor sites increases
    • Insulin: rises in pregnancy, but insulin resistance increases as well
    • Glucagon: levels are slightly raised in pregnancy, not as much as insulin levels
  47. Changes in pregnancy: Skin changes
    • Pruritic urticarial papules and plaques of pregnancy (PUPPP) **
    • Papular eruptions (prurigo gestationis and papular dermatitis)
    • Pruritis gravidarum**
    • Impetigo herpetiformis
    • Herpes gestationis
  48. PUPPP
    • pruritic urticarial papules and plaques of pregnancy
    • Onset: T2-T3
    • Severely pruritic
    • LEsions: erythematous urticarial papules and plaques
    • Distribution: abdomen, thighs, buttocks, occasionally arms and legs
    • Incidence: common (.25-1%)
    • No increased fetal morbidity/mortality
    • Intervention: topical steroids, antipruritic drugs
  49. Changes in pregnancy: Melanocyte-stimulating hormone
    • Increased in pregnancy causes:
    • Linea nigra: black line of the abdomen that runs from above the umbilicus to the pubis
    • Darkening of nipple and areola
    • Facial cholasma/melasma: brown hyperpigmentation in exposed areas such as face
    • Suntan acquired in pregnancy lasts longer than usual
  50. Changes in pregnancy: Estrogen effects
    • Spider nevi are common (branched growth of dilated capillaries on the skin)
    • Palmar erythema
  51. Changes in pregnancy: Corticosteroid effects
    Striae on the abdomen, breasts, etc.
  52. Changes in pregnancy: Fingernails
    Grow more rapidly during pregnancy
  53. Changes in pregnancy: Hair
    • Shed rate is reduced
    • Excess retained hair is often lost in the puerperium, secondary to maternal emotional stress
  54. Adaptations in pregnancy: Vagina
    • Vaginal epithelum hypertrophies
    • Increased quantity of glycogen-containing cells shed into vagina
    • Connective tissue decreases in collagen content; increase in water content
    • Vaginal becomes more acidic (pH = 4 to 5); hinders growth of most pathogens, favors growth of yeast
  55. Adaptations in pregnancy: Uterus
    • Hypertrophy and hyperplasia of myometrial smooth muscle, secondary to:
    • -steroid hormones
    • -Uterine distension and wall thinning
    • Term uterus weighs 1,100g with 20-fold increase in mass
  56. Adaptations in pregnancy: Round ligament
    • Increased length, muscular content, diameter
    • In pregnancy, may contract spontaneously, or in response to uterine movement
    • In labor: contractions of ligaments pulls the uterus forward
  57. Adaptations in pregnancy: Vascular supply of uterus
    • Nonpregnant: uterine artery
    • Pregnant: ovarian arteries contribute 20 to 30% of blood supply
    • Uterine arteries dilate to 1.5 times their diameter
  58. Adaptations in pregnancy: Cervix
    • Softening: accumulation of glycosaminoglycans and increased water content and vasculatiry
    • "cervical ripening": takes place over last few weeks of gestation
    • Antibacterial mucous plug of the cervix: within endocervical canal
  59. Adaptations in pregnancy: Uterine isthmus
    • uterine isthmus: small region of uterus that lies between the uterine corpus and the cervix
    • At 12 weeks: isthmus enlarges and thins
    • Labor: isthmus expands and is termed the lower uterine segment
  60. Conception: ovulation
    • ovum leaves the ovary, carried into the fallopian tube
    • surrounded by its zona pellucida
    • Oocyte has completed its first meiotic division and carries its first polar body
  61. Conception: fertilization
    • Occurs within 24hrs after ovulation in the ampulla (third of the tube adjacent the ovary
    • Fertilization: signals the ovum to complete meiosis II and to discharge an additional polar body
  62. Conception: preimplantation
    • Ovum remains in the ampulla for 80 hours, travels through isthmus of fallopian tube for 10 hours
    • Egg → multicellular blastomere
    • Blastomere passes into the uterine cavity
    • blastomere → blastocyst, floats in endometrial cavity for 90 to 150 hours
  63. Conception: Implantation
    • Day 5 to 6 of development: blastocyst adhere to the endometrium
    • After attachment, endometrium proliferates around the blastocyst
  64. Conception: Placentation
    • During week 2, cells in outer cell mass differentiate into trophoblasts
    • Trophoblastic shell forms initial boundary between embryo and the endometrium
    • Trophoblasts near the myometrium form placental disk; others form chorionic membranes
  65. Conception: Postimplantation
    • Endometrium or lining of uterus during pregnancy is termed decidua
    • Maternal RBCs may be seen in the trophoblastic lacunae in the second week postconception
  66. Embryology 
    timeline [wks]
    • Embryo development
    • wk 1: Early morula; no organ differentiation
    • wk 3: Double heart recognized
    • wk 4: initial organogenesis
    • wk 6: Genetic sex determined
    • wk 8: Sensory organ development and nondifferentiated gonadal development
    • Fetal development
    • wk 12: Brain configuration roughly complete, sex now specific, blood forming in marrow, external genitalia forming, uterus no longer bicornuate
    • wk 16: Fetus is active, sex determined by visual inspection, myelination of nerves, heart muscle well developed, vagina and anus open, ischium ossified
    • wk 20: Sternum ossifies
    • wk 24: Primitive respiratory movements
    • wk 28: Nails appear and testes at or below internal inguinal ring
    • wk 36: Earlobe soft with little cartilage, scrotum small with few rugae
    • wk 40: Earlobes stiffen by thick cartilage, scrotum well developed
  67. Developmental ages
    timeline [days]
    • 4: blastula
    • 7-12: implantation
    • 13: Primitive streak
    • 16: Neural plate
    • 19-21: First somite
    • 23-25: Closure of anterior neuropore
    • 25-27: Arms bud, closure of posterior neuropore
    • 28: Legs bud
    • 44: sexual differentiation
  68. Placenta
    blood supply
    • adapts over T2 and T3; primary producer of steroid hormones after 7 weeks' GA
    • Blood supply: arcuate and radial arteries during normal pregnancy is high with low resistance (resistance falls after 20 weeks)
  69. Multiple gestation
    • Division of embryos before differentiation of trophoblasts (< day 2 or 3): 2 chorions, 2 amnions
    • Division of embryos after trophoblast differentiation and before amnion formation (days 3 to 8): 1 placenta, 1 chorion, 2 amnions)
    • Division of embryos after amnion formation (day 8 to 13): 1 placenta, 1 chorion, 1 amnion
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  71. Pregnancy proteins: hCG
    • Source: placenta
    • Function: Maintains the corpus luteum; stimulates adrenal and placental steroidogenesis
  72. Pregnancy proteins: ACTH
    • Source: Trophoblasts
    • Function: Stimulates an increase in circulating maternal free cortisol
  73. Pregnancy proteins: hPL
    • Source: trophoblasts
    • Function: Antagonizes insulin; maternal glucose intolerance, lipolysis, proteolysis
  74. Pregnancy proteins: CRH
    • Source: placental tissue and decidua
    • Function: Stimulates placental ACTH release and participates in the surge of fetal glucocorticoids associated with late T3 fetal maturation
  75. Pregnancy proteins: Prolactin
    • Source: Decidualized endometrium
    • Function: Regulates fluid and electrolyte flux through the fetal membranes
  76. Pregnancy proteins: Alpha-Fetoprotein (AFP)
    • Source: Yould sac, fetal GI tract, fetal liver
    • Function: regulates fetal intravascular volume (osmoregulator)
    • -MSAFT peaks between 10 and 13 weeks' GA, then declines
    • -Detectable as early as 7 weeks' GA
    • MSAFP is decreased in  pregnancies with Down's syndrome
    • Amniotic fluid AFP and maternal serum (MSAFP) are elevated in association with neural tube defects and low in trisomy 21
  77. Pregnancy steroids: Estrogens
    • Function: estrogens affect uterine vasculature
    • Estradiol: maternal ovaries (wks 1 through 6); placenta after T1. during T3, low estradiol levels are associated with poor outcomes
    • Estrone: maternal ovaries, adrenals, and peripheral conversion for first 4 to 6 weeks; placenta therafter
    • Estriol: placenta (need living fetus)
  78. Pregnancy steroids: Progesterone
    • Source: corpus luteum before 6 weeks, placenta therafter (from LDL)
    • Function: affects tubal motility, endometrium, uterine vasculatur, parturition; inhibits T lymphocyte-mediated tissue rejection
    • *abortion will occur in 80% of women with progetserone levels under 10ng/mL
  79. Pregnancy steroids: Cortisol
    • Source: Decidual tissue
    • Function: Suppresses the maternal immune rejection response of the implanted coceptus
  80. Pregnancy steroids: LDL Cholesterol
    • Source: fetal adrenal gland
    • Function: regulatory precursor of corpus luteum progesterone production; lipoprotein utilized in fetal adrenal steroidogenesis
Card Set
OB Shelf - anatomy and physiology of pregnancy
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