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3.Maternal Physiology2009


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3.Maternal Physiology2009

  1. 1. <ul><li>PREGNANCY PHYSIOLOGY </li></ul><ul><li>Tianjin Medical University General Hospital </li></ul><ul><li>Obstetrics and Gynecology Department </li></ul><ul><li>Bai Xiaohong </li></ul>
  2. 2. review
  3. 3. review
  4. 4. <ul><li>Pregnancy (gestation) is the maternal condition of having a developing fetus in the body. </li></ul>
  5. 5. Diagnosis of the first trimester pregnancy
  6. 6. <ul><li>History and symptoms: </li></ul><ul><li>Amenorrhea </li></ul><ul><li>morning sickness (nausea and vomiting) </li></ul><ul><li>Bladder frequency </li></ul><ul><li>Sign </li></ul><ul><li>Change in the genital organs </li></ul><ul><li>Change in breasts </li></ul><ul><li>Assistant examnination </li></ul><ul><li>BBT </li></ul><ul><li>Pregnancy test </li></ul><ul><li>Ultrasound examination </li></ul>
  7. 7. <ul><li>Maternal physiologic adjustment to pregnancy are designed to support the requirements of fetal homeostasis and growth . </li></ul><ul><li>This is accomplished by remodeling maternal systems: </li></ul><ul><li>To deliver energy and growth substrates to the fetus </li></ul><ul><li>To remove inappropriate heat and waste products </li></ul><ul><li>Those maternal adaptation maintain a healthy enviroment for the fetus. </li></ul>
  8. 8. Maternal physiologic adjustment in pregnancy <ul><li>The physiology, biochemical, and anatomic changes that occur during pregnancy are extensive and may be systemic or local. </li></ul><ul><li>Most systems return to prepregnancy status within 6 weeks postpartum . </li></ul>
  9. 9. The fetus
  10. 10. <ul><li>The human conceptus from fertilization through the eighth week of pregnancy is termed an embryo ; from the eighth week until delivery, it is a fetus . </li></ul><ul><li>The estimated age of the fetus calculated from the first day of the last (normal) menstrual period (LMP), assuming a 28-day cycle. </li></ul><ul><li>The growth of the fetus may be conveniently described in units of 4 weeks’ gestational age , beginning with the first day of the LMP. </li></ul>Fetal growth and development
  11. 11. 8 weeks : the organ are beginning to form. 12 weeks : the finger and toes have nails, and the external genitalia may be recognizable.
  12. 12. 16 weeks : the sex is discernible as male or female. 20 weeks : movement have been perceived by the mother.
  13. 13. <ul><li>24 weeks : The weight is 600 g. Viability is reached by the 24th week, but survival at this stage is still relatively rare. </li></ul><ul><li>28 weeks : The weight is about 1000 g. The lungs are capable of breathing, but the surfactant content is low, survival is possible in some neonatal centers. </li></ul>
  14. 14. <ul><li>32 weeks : The weight is 1700 g. If born at this stage, about 5 of 6 infants survive. </li></ul>
  15. 15. 37 <ul><li>36 weeks : The weight is 2500 g and the length about 45 cm. The chances for survival are good. </li></ul><ul><li>40 weeks : The fetus averages 50 cm and 3000 g in weight. The head has a maximal transverse diameter of 9.5 cm. </li></ul>
  16. 16. The limits of the fetal role in maintaining fetal homeostasis are clear. <ul><li>The fetal lung and kidney appear to play no role in fetal respiration and excretion. </li></ul><ul><li>The fetus is capable of redistributing its cardiac output and oxygen delivery among different organs in response to physiologic demands. </li></ul>
  17. 17. The placenta,umbilical cord and amniotic fluid
  18. 18. The placenta <ul><li>A placenta may be defined as any intimate apposition or fusion of fetal organs to maternal tissues for the purpose physiologic exchange. </li></ul><ul><li>The basic parenchyma of all placentas is the trophoblast. When this becomes a membrane penetrated by fetal mesoderm, it is called the chorion. </li></ul>
  19. 19. <ul><li>When the trophoblast actually invades the maternal endometrium, a deciduate placenta results. </li></ul><ul><li>In human meternal blood comes into direct contact with the fetal trophoblast. </li></ul><ul><li>The human placenta may be described as a discoid, deciduate, hemochorial chorioallantoic placenta. </li></ul>
  20. 20. decidua Maternal blood chorion trophoblast
  21. 21. trophoblast Inner cell mass Destine to become the embryo blastocyst
  22. 22. <ul><li>A few hours after implantation,the trophoblast invades the endometrium and begin to produce hCG which is thought to be important in converting the normal corpus luteum into the corpus luteum of pregnancy. </li></ul>
  23. 23. Functions of the placenta <ul><li>The placenta is a complex organ of internal secretion, releasing numerous hormones (hCG, estrogen,placental proteins, human chorionic somatomammotropin hCS) and enzymes into the maternal blood.( endocrine function ) </li></ul>
  24. 24. <ul><li>It serves as the organ of transport for all fetal nutrient and metabolic products as well as for the exchange of oxygen and CO 2 .( metabolitic function ) </li></ul><ul><li>Referred to as a “barrier” to fetal transfer.( protective function ) </li></ul>
  25. 25. The umbilical cord <ul><li>Containing 2 umbilical arteries, one large umbilical vein. </li></ul><ul><li>The umbilical vein and 2 arteries twist around one another. </li></ul><ul><li>At birth the mature cord is 50-60 cm in length and 12mm in diameter. </li></ul>
  26. 26. The amniotic fluid <ul><li>In the first half of pregnancy, amniotic fluid volume appears to increase in association with the growth on the fetus. </li></ul><ul><li>The average volume of amniotic fluid at term is 800ml. </li></ul><ul><li>Amniotic fluid has a low specific gravity (1.008) and a pH of 7.2. </li></ul>
  27. 27. Function of the amniotic fluid <ul><li>It protect the fetus against severe injury. </li></ul><ul><li>provides a medium in which the fetus can move easily </li></ul><ul><li>May be a source of fetal nutrients </li></ul><ul><li>It is essential for fetal lung development in early pregnany </li></ul><ul><li>Being a valuable source for analysis of fetal tissue and fluid. </li></ul>
  28. 28. Maternal physiology during pregnancy
  29. 29. CONTENT <ul><li>Genital tract </li></ul><ul><li>Cardiovascular system  </li></ul><ul><li>Respiratory system  </li></ul><ul><li>Renal physiology  </li></ul><ul><li>Homeostasis of maternal energy substrates </li></ul><ul><li>Placental transfer of nutrients </li></ul><ul><li>Other endocrine change </li></ul><ul><li>Weight gain in pregnancy </li></ul>
  30. 30. Genital tract
  31. 31. Uterus Almost –solid structure thin-walled muscular organ Weighing about 70g 1100g Cavity of 10 ml or less 5L
  32. 32. Ovary <ul><li>Ovulation ceases during pregnancy and the maturation of new follicle is suspended. </li></ul>
  33. 33. Human chorionic gonadotrophin <ul><li>It is a glycoprotein that has biologic and immunologic similarities to luteinizing hormone from the pituitary. </li></ul><ul><li>hCG is produced by the syncytiotrophoblast of the placenta. </li></ul><ul><li>The measurement of the beta subunit of the hCG can detect pregnancy on day 11 after fertlization. </li></ul>
  34. 34. Cardiovascular system
  35. 35. Cardiovascular changes in pregnancy Peaks in early 2nd trimester, then stable until term ↑ 33%-45% Cardiac output Early 2nd trimester, then stable ↑ 10%-30% Stroke volume Early 2nd trimester, then stable ↑ 12-18 beats/min Heart rate All bottom at 20-24 wk, then rise gradually to prepregnancy values at term ↓ 4-6mm Hg ↓ 8-15mm Hg ↓ 6-10mm Hg Arterial blood pressures Systolic Diastolic Mean Timing Account of change Parameter
  36. 36. Cardiovascular system <ul><li> cardiac output </li></ul><ul><li> intravascular pressures </li></ul><ul><li> mechanical circulatory effects of gravid uterus </li></ul><ul><li> regional blood flow </li></ul><ul><li> control of cardiovascular changes </li></ul><ul><li> oxygen-carrying capacity of blood </li></ul>
  37. 37. <ul><li>Retention of sodium ( The total sodium accumulation averages 500 to 900 mEq by the time of delivery ) and water during pregnancy accounts for a total body water increase of 6 to 8 L ( 2/3 is located in the extravascular space ) . </li></ul>Cardiac output
  38. 38. <ul><li>The total blood volume increases by about 40% above nonpregnant levels, with wide individual variations. </li></ul>
  39. 39. <ul><li>The plasma volume rises as early as the sixth week of pregnancy and reaches a plateau by about 32 to 34 week’s gestation. The increase average 50% in singleton. </li></ul><ul><li>The red blood cell mass begins to increase at the start of the second trimester and continues to rise throughout pregnancy.By the time of delivery it is 20% to 35% above nonpregnant levels. </li></ul>
  40. 40. <ul><li>The disproportionate increase in plasma volume compared to the red cell volume results in hemodilution with a decreased hematocrit reading, sometimes referred to as physiologic anemia of pregnancy. </li></ul>
  41. 41. Cardiac output <ul><li>Cardiac output rises by the tenth week of gestation. </li></ul><ul><li>It reaches about 40% above nonpregnant levels by 20 to 24 weeks, after which there is little change. </li></ul>
  42. 42. Cardiac output <ul><li>The cardiovascular responses to exercise are altered during pregnancy. </li></ul><ul><li>For any given level of exercise, oxygen consumption is higher in pregnant than in nonpregnant women. </li></ul><ul><li>The cardiac output for given level of exercise is also increased during pregnancy compared to that seen in a nonpregnant state, and the maximum cardiac output is reached at lower levels of exercise. </li></ul>
  43. 43. Cardiac output <ul><li>It is not clear that any of the changes in hemodynamic responses to exercise are detrimental to mother and fetus. </li></ul><ul><li>But it suggests that maternal cardiac reserves are lowered during pregnancy and that shunting of blood away from the uterus might occur during or after exercise. </li></ul>
  44. 45. Intravascular pressures <ul><li>Systolic pressure falls only slightly during pregnancy, whereas diastolic pressure decreases more markedly; this decrease begins in the first trimester, reaches its nadir in midpregnancy, and returns toward nonpregnant levels by term. </li></ul>
  45. 46. <ul><li>These changes reflect the elevated cardiac output and reduced peripheral resistance that characterize pregnancy; toward the end of pregnancy, vasoconstrictor tone, and with it blood pressure, normally increases. </li></ul><ul><li>The normal rise of blood pressure toward prepregnant levels as term approaches must be recognized and the implications for the diagnosis of pre-eclampsia. </li></ul>Intravascular pressures
  46. 47. Mechanical circulatory effects of gravid uterus <ul><li>As pregnancy progresses, the enlarging uterus displaces and compresses various abdominal structures, including the iliac veins and inferior vena cava, with marked effects. </li></ul><ul><li>The supine position accentuates this venous compression, producing a fall in venous and hence cardiac output . </li></ul>
  47. 48. <ul><li>In most gravid women, a compensatory rise in peripheral resistance minimizes the fall in blood pressure. </li></ul><ul><li>In up to 10% of gravid women, a significant fall occurs in blood pressure accompanied by symptoms of nausea, dizziness, and even syncope. This supine hypotensive syndrome is relieved by changing position to the side. </li></ul>Mechanical circulatory effects of gravid uterus
  48. 49. Mechanical circulatory effects of gravid uterus <ul><li>The venous compression by the gravid uterus elevates pressure in veins that drain the legs and pelvic organs, thereby exacerbating varicose veins in the legs and vulva and causing hemorrhoids . </li></ul><ul><li>The rise in venous pressure is the major cause of the lower extremity edema that characterized pregnancy. </li></ul><ul><li>Because of venous compression, the rate of blood flow in the lower veins is also markedly reduced, causing a predisposition to thrombosis. </li></ul>
  49. 50. Regional blood flow <ul><li>Blood flow to most regions of the body increases and reaches a plateau relatively early in pregnancy. </li></ul><ul><li>Notable exception occur in the uterus, kidney, breast, and skin, in each of which blood flow increase with gestational age. </li></ul>
  50. 51. Regional blood flow <ul><li>Two of the major increases (those to the kidney and to the skin) serve purposes of elimination: the kidney of waste material and the skin of heat. </li></ul><ul><li>Both processes require plasma rather than whole blood, which gives point to disproportionate increase of plasma over red blood cells in the blood expansion. </li></ul>
  51. 52. Regional blood flow <ul><li>Early in pregnancy, renal blood flow increases to level approximately 30% above nonpregnant levels and remains unchanged as pregnancy advances. </li></ul><ul><li>This changes accounts for the increased creatinine clearance and lower serum creatine level. </li></ul>
  52. 53. Regional blood flow <ul><li>Engorgement of the breasts begins early in human pregnancy , and mammary blood flow increases 2 to 3 times toward the end of pregnancy. </li></ul><ul><li>The skin blood flow increases slightly during the third trimester, reaching 12% of cardiac output. </li></ul>
  53. 54. Regional blood flow <ul><li>The uterine blood increases from about 100mL/minute in the nonpregnant state (2% of cardiac output) to approximately 1200mL/minute at term (17% of cardiac output) . </li></ul><ul><li>Uterine blood flow, and thus gas and nutrient transfer, to the fetus is vulnerable. </li></ul>
  54. 55. Regional blood flow <ul><li>When maternal cardiac output falls, blood flow to the brain, kidneys, and heart is redistributed, thus shunting blood away from the uteroplacental circulation. </li></ul><ul><li>Similarly, changes in perfusion pressure can lead to decreases in uterine blood flow. </li></ul><ul><li>Because the uerine vessels are maximally dilated during pregnancy, little autoregulation can occur to improve uterine blood flow. </li></ul>
  55. 56. Control of cardiovascular changes <ul><li>The precise mechanisms accounting for the cardiovascular changes in pregnancy have not been fully elucidated. </li></ul><ul><li>The rise in cardiac output and fall in peripheral resistance during pregnancy might be explained in terms of the circulatory response to an arteriovenous shunt, represented by the uteroplacental circulation. </li></ul>
  56. 57. Control of cardiovascular changes <ul><li>A unifying hypothesis suggests that the changes in circulating steroid hormones in combination with changes in production of vasodilatory prostaglandins, atrial natriuretic peptide, nitric oxide, and aldosterone affect venous distensibility and arterial tone. </li></ul>
  57. 58. Oxygen-carrying capacity of blood <ul><li>Plasma volume expands proportionately more than red blood cell volume, leading to a fall in hematocrit. </li></ul><ul><li>Despite the relatively low “optimal” hematocrit, the arteriovenous oxygen difference in pregnancy is below nonpregnant levels. </li></ul>
  58. 59. <ul><li>This supports the concept that hemoglobin concentration in pregnancy is more than sufficient to meet oxygen-carrying requirements . </li></ul>
  59. 60. Respiratory system
  60. 61. The major respiratory changes in pregnancy <ul><li>The mechanical effects of the enlarging uterus </li></ul><ul><li>The increased total body oxygen consumption </li></ul><ul><li>The respiratory stimulant effect of progesterone </li></ul>
  61. 62. No significant change Progressive rise throughout pregnancy of 0.1-0.2L Lowered by about 15%(0.55L in late pregnancy compared with 0.65L postpartum) Falls considerably (0.77L in late pregnancy compared with 0.96L postpartum) Unchanged ,expect for possibly a small terminal diminution Increased by about 5% Lowered by about 18% Increased by about 40% as a result of the increased tidal volume and unchanged respiratory rate Respiratory rate Tidal volume Expiratory reserve volume Residual volume Vital capacity Inspiratory capacity Functional residual capacity Minute ventilation Change in Pregnancy Test Lung volumes and capacities in pregnancy
  62. 63. <ul><li>Diaphragm at rest rises to a level of 4 cm above its usual resting position. </li></ul><ul><li>The chest enlarges in transverse diameter by about 2.1cm. </li></ul><ul><li>The subcostal angle increases from an average of 68.5 degrees to 103.5 degrees during the latter part of gestation. </li></ul>
  63. 64. <ul><li>As pregnancy progresses, the enlarging uterus elevates the resting position of the diaphragm. </li></ul><ul><li>This results in less negative intrathoracic pressure and a decreased resting lung volume, that is, a decrease in functional residual capacity (FRC). </li></ul>
  64. 65. <ul><li>The enlarging uterus produces no impairment in diaphragmatic or thoracic muscle motion. </li></ul><ul><li>The vital capacity (VC) remains unchanged. </li></ul>
  65. 66. Oxygen consumption and ventilation <ul><li>Total body oxygen consumption increases about 15% to 20% in pregnancy. </li></ul><ul><li>Half of this increase is accounted for by the uterus and its contents. </li></ul><ul><li>The remainder is accounted for mainly by increased maternal renal and cardiac work. </li></ul><ul><li>Smaller increments are due to work of the respiratory muscles and the breasts. </li></ul>
  66. 67. Oxygen consumption and ventilation <ul><li>A rise in oxygen consumption is accompanied by cardiorespiratory responses that facilitate oxygen delivery. </li></ul><ul><li>Elevations in cardiac output and alveolar ventilation keep pace with the rise in oxygen consumption, the arteriovenousoxygen different and the arterial partial pressure of Pco 2 respectively,remain unchanged. </li></ul><ul><li>The arteriovenous oxygen difference and arterial Pco 2 both fall. The fall in Pco 2 ,by definition, indicates hyperventilation. </li></ul>
  67. 68. <ul><li>The rise in minute ventilation reflects an approximate 40% increase in tidal volume(TV) at term; the respiratory rate does not change during pregnancy. </li></ul>
  68. 69. Oxygen consumption and ventilation <ul><li>Such increased respiratory center sensitivity to carbon dioxide CO2 is characteristic of pregnancy and probably accounts for the hyperventilation of pregnancy. </li></ul>
  69. 70. Oxygen consumption and ventilation <ul><li>In summary, both at rest and with exercise, minute ventilation and , to a lesser extent, oxygen consumption are increased during pregnancy over the nonpregnant control values. </li></ul><ul><li>The respiratory stimulating effect of progesterone is probably responsible for the disproportionate increase in minute ventilation over oxygen consumption. </li></ul>
  70. 71. Alveolar-arterial gradient and arterial blood gas measurements <ul><li>Pregnancy is characterized by hyperventilation (the arterial Pco 2 falls to a level of 27 to 32 mm Hg) and associated respiratory alkalosis. </li></ul><ul><li>Renal compensatory bicarbonate excretion leads to a final pH between 7.40 and 7.45. </li></ul>
  71. 72. Alveolar-arterial gradient and arterial blood gas measurements <ul><li>When alveolar Pco 2 falls during hyperventilation, alveolar partial pressure of oxygen (Po 2 ) shows a corresponding rise, leading to a rise in arterial Po 2. This occurs in pregnancy ; in the first trimester, the mean arterial Po 2 may be 106 to 108 mm Hg. </li></ul>
  72. 73. Alveolar-arterial gradient and arterial blood gas measurements <ul><li>There is a slight downward trend in arterial Po 2 as pregnancy proceeds. </li></ul><ul><li>This reflects, at least in part, an increased alveolar-arterial gradient, possibly resulting from the decrease in FRC, which leads to a ventilation-perfusion mismatch. </li></ul>
  73. 74. Renal physiology
  74. 75. Anatomic changes in the urinaty tract
  75. 76. <ul><li>The urinary collecting system, including the calyces, renal pelves, and ureters, undergoes marked dilation in pregnancy, as is readily seen on intravenous urograms. </li></ul><ul><li>The dilation is generally more prominent on the right side; it begins in the first trimester, is present until the 12 th to 16 th postpartum week. </li></ul>
  76. 77. <ul><li>This occurrence probably reflects the influence of both humoral and physical factors. </li></ul><ul><li>Progesterone appears to produce smooth muscle relaxation in various organs, including the ureter. </li></ul><ul><li>As the uterus enlarges , partial obstruction of the ureter occurs at the pelvic brim in both the supine and the upright positions. </li></ul>
  77. 78. Renal blood flow and glomerular filtration rate
  78. 79. <ul><li>Renal plasma flow and the glomerular filtration rate (GFR) increase early in pregnancy, achieve a plateau at about 40% above nonpregnancy levels by midgestation, and then remain unchanged to term. </li></ul><ul><li>The elevated GFR is reflected in lower serum levels of creatinine and urea nitrogen . </li></ul>
  79. 80. Renal tubular function <ul><li>Although 500 to 900 mEq of sodium is retained during pregnancy, sodium balance is maintained with exquisite precision during pregancy. </li></ul><ul><li>Only 20 to 30 mEq of sodium is retained every week. </li></ul>
  80. 81. Renal tubular function <ul><li>Pregnant women also maintain fluid balance with no change in the concentrating or diluting ability of the kidney. </li></ul><ul><li>Plasma osmolarity is reduced by approximately 10 mOsm/Kg of water. </li></ul><ul><li>Potassium metabolism during pregnancy is unchanged, although about 350 mEq of potassium is retain during pregnancy for fetoplacental development and expansion of maternal red cell mass. </li></ul>
  81. 82. Renal tubular function <ul><li>Pregnancy causes compensated respiratory alkalosis with chronic losses of renal bicarbonate. </li></ul><ul><li>These reductions in the renal buffering capacity predispose pregnant women to severe metabolic acidosis. </li></ul>
  82. 83. Fluid volumes <ul><li>The maternal extracellular volume, which consists of intravascular and interstitial components, increases throughout pregnancy, leading , in effect, to a state of physiologic extracellular hypervolemia . </li></ul><ul><li>The intravascular volume, which consists of plasma and red cell components, increases approximately 50% during pregancy. </li></ul><ul><li>Maternal interstitial volume shows its greatest increase in the last trimester. </li></ul>
  83. 84. Renin-angiotensin system in pregnancy <ul><li>The elements of the renin-angiotensin system are markedly altered in pregnancy. </li></ul><ul><li>Plasma concentrations of renin, renin substrate, and angiotensin are increased. </li></ul><ul><li>Renin levels remain elevated throughout pregnancy. </li></ul><ul><li>The uterus, like the kidney, can produce renin, and extremely high concentrations of renin occur in the amniotic fluid. </li></ul><ul><li>The role played by renin is not clear. </li></ul>
  84. 85. Homeostasis of maternal energy substrates
  85. 86. <ul><li>In pregnancy, the insulin responses to glucose stimulation is augment. </li></ul>Insulin effects and glucose metabolism
  86. 87. Insulin effects and glucose metabolism <ul><li>Glycogen synthesis and storage by the liver increases, and gluconeogenesis is inhibited. </li></ul><ul><li>After early pregnancy, insulin resistance emerges, so glucose tolerance is impaired. </li></ul><ul><li>The fall in serum glucose for a given dose of insulin is reduced compared with the response in earlier pregnancy. Elevation of circulating glucose is prolonged after meals, although fasting glucose remains reduced, as in the early pregnancy. </li></ul>
  87. 88. <ul><li>A variety of humoral factors have been suggested to account for the anti-insulin environment of the latter part of pregnancy. </li></ul><ul><li>Perhaps the most important is human placental lactogen (hPL), which antagonizes the peripheral effects of insulin. </li></ul><ul><li>Progesterone may exert some anti-insulin effects. </li></ul><ul><li>Levels of unbound cortisol are also increase. </li></ul>
  88. 89. Lipid metabolism <ul><li>The potentiated anabolic effects of insulin that characterized early pregnancy lead to the inhibition of lipolysis . </li></ul><ul><li>During the second half of pregnancy, however, probably as a result of rising hPL levels, lipolysis is augmented , and the plasma concentration of free fatty acids after an overnight fast is elevated. </li></ul>
  89. 90. Placental transfer of nutrients <ul><li>The transfer of substances across the placenta occurs by several mechanisms, including simple diffusion , facilitated diffusion , and active transport . </li></ul><ul><li>Several physiochemical factors, such as molecular size, degree of ionization, and lipid solubility, affect the rate of diffusion. </li></ul><ul><li>Substances with molecular weights greater than 1000 daltons, such as polypeptides and proteins, cross the placenta slowly. </li></ul>
  90. 91. <ul><li>Glucose is transported by facilitated diffusion, leading to rapid equilibrium with only a small maternal-fetal gradient. Glucose is the main energy substrate of the fetus although amino acids and lactate may contribute up to 25% of fetal oxygen consumption. </li></ul><ul><li>Amino acids are actively transported across the placenta, making fetal levels higher than maternal levels. </li></ul><ul><li>Free fatty acids diffuse passively across the placenta, and fetal levels are lower than maternal levels. </li></ul>
  91. 92. Other endocrine changes
  92. 93. Thyroid <ul><li>The thyroid gland undergoes moderate enlargement during pregnancy.This is not due to elevation of TSH which remains unchanged. </li></ul><ul><li>Thyroxine-binding globulin (TBG) is increased during pregnancy because the high estrogen levels induce increased hepatic synthesis. </li></ul><ul><li>Thyroid hormones do not cross the placenta . </li></ul>
  93. 94. Adrenal <ul><li>Adrenocorticotropic hormone ( ACTH ) and plasma cortisol levels are both elevated from 3 months’ gestation to delivery. </li></ul><ul><li>The mean unbound level of cortisol is elevated in pregnancy. </li></ul>
  94. 95. Weight gain in pregnancy
  95. 96. <ul><li>The average weight gain in pregnancy uncomplicated by generalized edema is 12.5 Kg. </li></ul><ul><li>The products of conception constitute only about 40% of the total maternal weight gain. </li></ul>