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  • Muscles and joints shift and jostle.

  • The heart's pounding rhythm speeds up. Blood roars through arteries and veins.

  • Over the course of a pregnancy, every organ in the body changes.

  • Ignited by a range of hormones,

  • these changes begin as soon as pregnancy begins.

  • Just days after fertilization, the embryo implants in the lining of the uterus.

  • Because its DNA doesn't exactly match the mother's,

  • the immune system should theoretically recognize it as an invader,

  • attack, and destroy it, like it would bacteria or other harmful microbes.

  • That's the challenge: the mother's immune system

  • needs to protect both her and the fetus, but can't act as it usually does.

  • What happens is not as simple as decreasing the immune response.

  • Instead, it's a complex interaction we're just beginning to understand,

  • involving many different types of immune cells

  • some of which seem to protect the fetus from attack by other immune cells.

  • The body also creates an antibacterial plug made of mucus on the cervix,

  • which keeps germs away and stays sealed until labor.

  • As a pregnancy progresses,

  • the uterus expands upward and outward with the growing fetus.

  • To make room, hormones called progesterone and relaxin

  • signal muscles to loosen.

  • The muscles that propel food and waste through the digestive tract also loosen,

  • which makes them sluggish,

  • causing constipation as passage through the tract slows down.

  • Loosened muscles at the top of the stomach

  • might allow acid to escape into the esophagus and throat,

  • causing heartburn and reflux.

  • These changes can worsen morning sickness,

  • which is caused in part by hormone HCGand can also happen at other times of day.

  • As the uterus grows, it pushes on the diaphragm,

  • the muscle that expands and contracts the chest with each breath.

  • This limits the diaphragm's range.

  • To compensate, the hormone progesterone acts as a respiratory stimulant,

  • making the pregnant woman breathe faster so both she and the baby

  • can both get enough oxygen with less lung capacity.

  • This all may leave the pregnant woman feeling short of breath.

  • Meanwhile, the kidneys make more erythropoietin,

  • a hormone that increases red blood cell production.

  • The kidneys also keep extra water and salt rather than filtering it out into urine

  • to build up the volume of the blood.

  • A pregnant woman's blood volume increases by 50% or more.

  • But it's also a bit diluted,

  • because it only has 25% more red blood cells.

  • Usually, the body makes blood cells using iron from our food.

  • But during pregnancy, the fetus is also building its own blood supply

  • from nutrients in the mother's food

  • leaving less iron and other nutrients for the mother.

  • The heart has to work extra hard to pump all this blood

  • through the body and placenta.

  • A pregnant woman's heart rate increases,

  • but we don't fully understand how blood pressure changes in a healthy pregnancy

  • an important area of research,

  • because some of the most serious complications

  • are related to the heart and blood pressure.

  • The expanding uterus may press on veins

  • causing fluid buildup in the legs and feet.

  • If it presses on a large vein called the inferior vena cava,

  • it might interfere with blood returning to the heart,

  • causing a dizzying drop in blood pressure after standing for too long.

  • Some of these changes start to reverse even before birth.

  • Shortly before delivery, the fetus drops down,

  • decreasing the pressure on the diaphragm

  • and allowing the pregnant woman to take deeper breaths.

  • During labor and birth,

  • much of the extra fluid in the body is lost when the water breaks.

  • The uterus shrinks back down in the weeks after birth.

  • Like the rest of the body, pregnancy affects the brain

  • but its effects here are some of the least understood.

  • Recent studies show differences in brain scans

  • after pregnancy and early parenting,

  • and suggest that these changes are adaptive.

  • That means they could help with parenting skills,

  • such as an increased ability to read facial cues since babies can't talk.

  • The lack of information about pregnancy's effects on the brain

  • highlights a general truth: historically, almost all the research around pregnancy

  • has focused on the fetus, rather than pregnant women.

  • Experiences of pregnancy vary widely,

  • both within the range of healthy pregnancies

  • and due to complicating health conditionsnew research will help us understand why,

  • and develop effective treatments where necessary.

  • In the meantime, every pregnancy is different,

  • and it's important to consult a doctor with any specific questions.

  • Today, we're turning an exciting corner,

  • as more research is devoted to the astounding biology of pregnancy.

Muscles and joints shift and jostle.

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The surprising effects of pregnancy

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    林宜悉 posted on 2020/12/07
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