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← The surprising effects of pregnancy

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Showing Revision 1 created 09/30/2020 by lauren mcalpine .

  1. Muscles and joints shift and jostle.
  2. The heart’s pounding rhythm speeds up.
    Blood roars through arteries and veins.
  3. Over the course of a pregnancy,
    every organ in the body changes.
  4. Ignited by a range of hormones,
  5. these changes begin
    as soon as pregnancy begins.
  6. Just days after fertilization, the embryo
    implants in the lining of the uterus.

  7. Because its DNA doesn’t exactly match
    the mother’s,
  8. the immune system should theoretically
    recognize it as an invader,
  9. attack, and destroy it, like it would
    bacteria or other harmful microbes.
  10. That’s the challenge:
    the mother’s immune system
  11. needs to protect both her and the fetus,
    but can’t act as it usually does.
  12. What happens is not as simple
    as decreasing the immune response.
  13. Instead, it’s a complex interaction
    we’re just beginning to understand,
  14. involving many different types
    of immune cells—
  15. some of which seem to protect the fetus
    from attack by other immune cells.
  16. The body also creates an antibacterial
    plug made of mucus on the cervix,
  17. which keeps germs away
    and stays sealed until labor.
  18. As a pregnancy progresses,

  19. the uterus expands upward and outward
    with the growing fetus.
  20. To make room, hormones
    called progesterone and relaxin
  21. signal muscles to loosen.
  22. The muscles that propel food and waste
    through the digestive tract also loosen,
  23. which makes them sluggish,
  24. causing constipation as passage
    through the tract slows down.
  25. Loosened muscles
    at the top of the stomach
  26. might allow acid to escape
    into the esophagus and throat,
  27. causing heartburn and reflux.
  28. These changes can worsen morning sickness,
  29. which is caused in part by hormone HCG—
    and can also happen at other times of day.
  30. As the uterus grows,
    it pushes on the diaphragm,

  31. the muscle that expands and contracts
    the chest with each breath.
  32. This limits the diaphragm’s range.
  33. To compensate, the hormone progesterone
    acts as a respiratory stimulant,
  34. making the pregnant woman breathe
    faster so both she and the baby
  35. can both get enough oxygen
    with less lung capacity.
  36. This all may leave the pregnant woman
    feeling short of breath.
  37. Meanwhile, the kidneys
    make more erythropoietin,

  38. a hormone that increases
    red blood cell production.
  39. The kidneys also keep extra water and salt
    rather than filtering it out into urine
  40. to build up the volume of the blood.
  41. A pregnant woman’s blood volume
    increases by 50% or more.
  42. But it’s also a bit diluted,
  43. because it only has 25%
    more red blood cells.
  44. Usually, the body makes blood cells
    using iron from our food.
  45. But during pregnancy, the fetus
    is also building its own blood supply
  46. from nutrients in the mother’s food—
  47. leaving less iron and other nutrients
    for the mother.
  48. The heart has to work extra hard
    to pump all this blood

  49. through the body and placenta.
  50. A pregnant woman’s heart rate increases,
  51. but we don’t fully understand how blood
    pressure changes in a healthy pregnancy—
  52. an important area of research,
  53. because some of the most serious
    complications
  54. are related to the heart
    and blood pressure.
  55. The expanding uterus may press on veins—
  56. causing fluid buildup
    in the legs and feet.
  57. If it presses on a large vein
    called the inferior vena cava,
  58. it might interfere with blood
    returning to the heart,
  59. causing a dizzying drop in blood pressure
    after standing for too long.
  60. Some of these changes start
    to reverse even before birth.

  61. Shortly before delivery,
    the fetus drops down,
  62. decreasing the pressure on the diaphragm
  63. and allowing the pregnant woman
    to take deeper breaths.
  64. During labor and birth,
  65. much of the extra fluid in the body
    is lost when the water breaks.
  66. The uterus shrinks back down
    in the weeks after birth.
  67. Like the rest of the body,
    pregnancy affects the brain—

  68. but its effects here are some
    of the least understood.
  69. Recent studies show differences
    in brain scans
  70. after pregnancy and early parenting,
  71. and suggest that these changes
    are adaptive.
  72. That means they could help
    with parenting skills,
  73. such as an increased ability to read
    facial cues since babies can’t talk.
  74. The lack of information about pregnancy’s
    effects on the brain

  75. highlights a general truth: historically,
    almost all the research around pregnancy
  76. has focused on the fetus,
    rather than pregnant women.
  77. Experiences of pregnancy vary widely,
  78. both within the range
    of healthy pregnancies
  79. and due to complicating health conditions—
    new research will help us understand why,
  80. and develop effective treatments
    where necessary.
  81. In the meantime,
    every pregnancy is different,
  82. and it’s important to consult a doctor
    with any specific questions.
  83. Today, we’re turning an exciting corner,
  84. as more research is devoted
    to the astounding biology of pregnancy.