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MATERNAL PHYSIOLOG CHANGES (Part 02)

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Genitourinary System

  1. increased GFR 50% (therefore decreased BUN and serum creatinine) but no change in urine output because of increased reabsorption in tubules glycosuria can be physiologic; with increase in GFR the threshold for glucose reabsorption can be surpassed
  2. increased urinary frequency
  3. physiologic dilatation of ureters and renal pelvis (R > L) due to progesterone-induced smooth muscle relaxation and uterine enlargement
  4. increased incidence of UTI and pyelonephritis due to stasis
    asymptomatic bacteriuria more likely to become a clinically significant infection (i.e. pyelonephritis) in pregnancy and therefore should be treated

Endocrine System



  1.  estrogen
    1. main estrogen is estradiol (E2)
    2. production involves an intricate pathway, requiring maternal, placental and fetal contributions
    3. sudden decline may indicate fetal compromise
  2.  progesterone
    1. produced by corpus luteum during first 7 weeks, thereafter synthesized by the placenta
    2. maintains the endometrium
    3. absolutely necessary for continuation of pregnancy

  3.  Human chorionic gonadotropin (hCG)
  1. produced by placental trophoblastic cells peptide hormone composed of two subunits: alpha (common to all glycoproteins) and beta (specific to hCG)
  2. has LH-like actions: maintains the corpus luteum
  3. serum β-hCG positive 8-9 days after ovulation
  4. plasma levels double every 1-2 days, peak (8-10 weeks) and  then fall to a plateau until delivery
  5. rule of 10's
    10 IU at time of missed menses
    100 000 IU at 10 weeks (peak)
    10 000 IU at term
  6. levels below expected by dates suggest an ectopic pregnancy, abortion or wrong dates
  7. levels higher than expected suggest multiple gestation, molar pregnancy, trisomy 21, or wrong dates

  4.   thyroid
  1. moderate enlargement and increased basal metabolic rate
  2. increased total thyroxine and thyroxine binding globulin (TBG)
  3. free thyroxine index and TSH levels are normal

  5.  adrenal  : maternal cortisol rises throughout pregnancy (total and free)

  6.  prolactin
  • produced by maternal pituitary in response to increasing estrogen in pregnancy
  • stimulates lactation
  7. relaxin
  • produced by the corpus luteum/ovary
  • relaxes symphysis pubis and other pelvic joints
  • helps soften and dilate the cervix
  • inhibits uterine contraction
Ca++ metabolism

  1. total maternal Ca decreased due to decreased albumin
  2. free ionized (i.e. active) proportion remains the same due to increased PTH which results in increased bone resorption and gut absorption  bone turnover increased but no loss of bone density because estrogen counteracts the PTH effect by inhibiting resorption

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MATERNAL PHYSIOLOG CHANGES (Part 02) MATERNAL PHYSIOLOG CHANGES (Part 02) Reviewed by Radiology Madeeasy on December 26, 2010 Rating: 5
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