The body must change its physiological and homeostatic mechanisms in pregnancy to ensure the fetus is provided for. Increases in blood sugar, breathing and cardiac output are all required.
Hormonal changes
Levels
of progesterone and oestrogens rise continually throughout pregnancy,
suppressing the hypothalamic axis and subsequently the menstrual cycle.
The woman and the placenta also produce many hormones.
Prolactin levels increase due to maternal Pituitary gland enlargement by 50%. This mediates a change in the structure of the Mammary gland from ductal to lobular-alveolar. Parathyroid hormoneis increased due to increases of calcium uptake in the gut and reabsorption by the kidney. Adrenal hormones such as cortisol and aldosterone also increase.
Placental lactogen is
produced by the placenta and stimulates lipolysis and fatty acid
metabolism by the woman, conserving blood glucose for use by the fetus.
It also decreases maternal tissue sen
sitivity to insulin, resulting in gestational diabetes.
sitivity to insulin, resulting in gestational diabetes.Musculoskeletal changes
The
body's posture changes as the pregnancy progresses. The pelvis tilts
and the back arches to help keep balance. Poor posture occurs naturally
from the stretching of the woman's abdominal muscles as the fetus grows.
These muscles are less able to contract and keep the lower back in
proper alignment. The pregnant woman has a different pattern of gait.
The step lengthens as the pregnancy progresses, due to weight gain and
changes in posture. On average, a woman's foot can grow by a half size
or more during pregnancy. In addition, the increased body weight of
pregnancy, fluid retention, and weight gain lowers the arches of the
foot, further adding to the foot's length and width. The influences of
increased hormones such as estrogen and relaxin initiate the remodeling of soft tissues, cartilage and ligaments. Certain skeletal joints such as the symphysis pubis andsacroiliac widen or have increased laxity.
Physical changes
Weight
is gained during pregnancy due to increased appetite, fat deposition,
and growth of the reproductive organs and fetus, as well as increased
blood volume and water retention. Anywhere from 5 pounds (2.3 kg) to
over 100 pounds (45 kg) can be gained during pregnancy. In America, the
doctor-recommended weight gain range is 25 pounds (11 kg) to 35 pounds
(16 kg), less if the woman is overweight, more (up to 40 pounds (18 kg))
if the woman is underweight.
Other
physical changes during pregnancy include breasts increasing two cup
sizes. Also areas of the body such as the forehead and cheeks (known as
the 'mask of pregnancy') become darker due to the increase of melanin
being produced.
The female body experiences many changes as the fetus grows through each trimester as shown and discussed in this pregnancy video. Two women at different stages in their pregnancy illustrate what has happened to their bodies.
Cardiovascular changes
Blood
volume increases by 40% in the first two trimesters. This is due to an
increase in plasma volume through increased aldosterone. Progesterone
may also interact with the aldosterone receptor, thus leading to
increased levels. Red blood cell numbers increase due to increased erythropoietin levels.
Cardiac
function is also modified, with increase heart rate and increased
stroke volume. A decrease in vagal tone and increase in sympathetic tone
is the cause. Blood volume increases act to increase stroke volume of
the heart via Starling's law. After pregnancy the change in stroke volume is not reversed. Cardiac output rises from 4 to 7 litres in the 2nd trimester
Blood pressure also fluctuates. In the first trimester it falls. Initially this is due to decreased sensitivity to angiotensin and
vasodilation provoked by increased blood volume. Later, however, it is
caused by decreased resistance to the growing uteroplacental bed.
Respiratory changes
Decreased
functional residual capacity is seen, typically falling from 1.7 to
1.35 litres, due to the compression of the diaphragm by the uterus.
Tidal volume increases, from 0.45 to 0.65 litres, giving an increase in
pulmonary ventilation. This is necessary to meet the increased oxygen
requirement of the body, which reaches 50ml/min - 20ml of which goes to
reproductive tissues.
Progesterone may act centrally on chemoreceptors to reset the set point to
a lower partial pressure of carbon dioxide. This maintains an increased
respiration rate even at a decreased level of carbon dioxide.
Metabolic changes
An
increased requirement for nutrients is given by fetal growth and fat
deposition. Changes are caused by steroid hormones, lactogen and
cortisol.
Maternal
insulin resistance can lead to gestational diabetes. Increase liver
metabolism is also seen, with increased gluconeogenesis to increase
maternal glucose levels.
Renal changes
Renal
plasma flow increases, as does aldosterone and erthropoietin production
as discussed. The tubular maximum for glucose is reduced, which may
precipitate gestational diabetes.
Management
Prenatal medical care is of recognized value throughout the developed world. Periconceptional Folic acid supplementation is the only type of supplementation of proven efficacy.
Nutrition
A balanced, nutritious diet is an important aspect of a healthy pregnancy. Eating a healthy diet, balancing carbohydrates, fat, and proteins, and eating a variety of fruits and vegetables,
usually ensures good nutrition. Those whose diets are affected by
health issues, religious requirements, or ethical beliefs may choose to
consult a health professional for specific advice.
Adequate periconceptional folic acid (also called folate or Vitamin B9) intake has been proven to limit fetal neural tube defects, preventing spina bifida, a very serious birth defect.
The neural tube develops during the first 28 days of pregnancy,
explaining the necessity to guarantee adequate periconceptional folate
intake. Folates (from folia, leaf) are abundant in spinach (fresh, frozen, or canned), and are also found in green vegetables, salads, citrus fruit and melon, chickpeas (i.e. in the form of hummus or falafel), and eggs. In the United States and Canada, most wheat products (flour, noodles) are fortified with folic acid.
Several micronutrients are
important for the health of the developing fetus, especially in areas
of the world where insufficient nutrition is prevalent. In developed
areas, such as Western Europe and the United States, certain nutrients such as Vitamin D and calcium, required for bone development, may require supplementation.
There is some evidence that long-chain omega-3 (n-3) fatty acids have
an effect on the developing fetus, but further research is required. At
this time, supplementing the diet with foods rich in these fatty acids
is not recommended, but is not harmful.
Dangerous bacteria or parasites may contaminate foods, particularly listeria and toxoplasma, toxoplasmosis agent.
Careful washing of fruits and raw vegetables may remove these
pathogens, as may thoroughly cooking leftovers, meat, or processed meat.
Soft cheeses may contain listeria; if milk is raw the risk may
increase. Cat feces pose a particular risk of toxoplasmosis. Pregnant
women are also more prone to catching salmonella infections
from eggs and poultry, which should be thoroughly cooked. Practicing
good hygiene in the kitchen can reduce these risks.