Metabolic Changes In Pregnancy.docx

Metabolic Changes  

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Numerous and intense o 3rd trimester: BMR rises by 20% (+10% with twins) Total pregnancy energy demand ~77000 kcal o 1st trimester: 85 kcal/d o 2nd: 285 kcal/d o 3rd 475 kcal/d Pregnant women accumulate fat mass despite increased total energy expenditure and without significant change in energy intake o Ensures more efficient energy storage

Weight gain     

~12.5 kg or 27.5 lb Uterus Breasts Blood and ECF volumes A smaller fraction results from metabolic alterations that promote accumulation of cellular water, fat, and protein, which are so-called maternal reserves

Water Metabolism  Greater water retention o Pitting edema of ankles and legs  Greater venous pressure below uterus as a result of partial vena cava occlusion  Decline in interstitial colloid osmotic pressure  Drop in plasma osmolality of 10 mOsm/kg o Develops in early pregnancy o Induced by a reset of osmotic thresholds for thirst and vasopressin secretion

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At term, water content of fetus, placenta, and amniotic fluid = ~3.5 L o Maternal blood from uterus and breast growth= 3.0 L o The minimum amount of extra water that the average woman accrues during normal pregnancy= ~6.5 L = 14.3 lb  Accumulation of total body water, fat mass, initial maternal weight, and weight gained during pregnancy are highly associated with neonatal birthweight o Over-nourished mother= over-sized child o Protein Metabolism  Product of conception, uterus, and maternal blood are rich in protein  At term, normally grown fetus + placenta weighs= 4kg o Contains 500g proteins o Remaining 500g is added to the uterus (contractile protein), breast (glands), and to maternal blood (Hb and plasma proteins)  Fetal amino acid > Maternal amino acid (facilitated transport)  Maternal protein intake does not appear to be a critical determinant for birthweight among wellnourished women Carbohydrate Metabolism  Mild fasting hypoglycemia, postprandial hyperglycemia, and hyperinsulinemia in response to glucose ingestion o Suggests a pregnancy- induced state of peripheral glucose resistance to ensure a postprandial supply of glucose to the fetus o Hepatic gluconeogenesis is augmented during both diabetic and nondiabetic pregnancies, particularly in the third trimester  Insulin sensitivity in late normal pregnancy is 30-70% lower than non-pregnant women o Pregnancy-related hormones such as progesterone, placentally derived growth hormone, prolactin, and cortisol; cytokines such as tumor necrosis factor; and hormones derived from central adiposity, particularly leptin and its interplay with prolactin, all have a role in the insulin resistance of pregnancy.  Accelerated starvation o pregnant woman changes from a postprandial state characterized by elevated and sustained glucose levels to a fasting state characterized by decreased plasma glucose and some amino acids. o Plasma concentrations of free fatty acids, triglycerides, and cholesterol are also higher in the fasting state.

Fat Metabolism  Increased concentrations of lipids, lipoproteins, and apolipoproteins  Maternal hyperlipidemia o Caused by increased insulin resistance and estrogen stimulation during pregnancy  First two trimester o Augmented lipid synthesis and food intake contribute to maternal fat accumulation  Third trimester o Fat storage declines o Due to  Enhanced lipolytic activity and decreased lipoprotein lipase activity  Reducing circulating TAG uptake into adipose tissue  Leptin o primarily secreted by adipose tissue in nonpregnant humans. o It plays a key role in body fat and energy expenditure regulation and in reproduction. For example, leptin is important for implantation, cell proliferation, and angiogenesis o Deficiency: anovulation and infertility o Mutations: obesity o Rise and peak during 2nd trimester and plateau until term o Falls after delivery o Fetal leptin is important for the development of several organs that include the pancreas, kidney, heart, and brain Electrolyte and Mineral  1000 mEq of sodium and 300 mEq of potassium are retained o Glomerular filtration of Na and K are increased but excretion of these electrolytes is unchanged as a result of enhanced tubular resorption o Total serum calcium levels decline during pregnancy  Follows lowered plasma albumin concentrations and consequent decrease in the amount of circulating protein-bound nonionized calcium  But serum ionized calcium levels remain unchanged

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 Dietary intake is necessary to prevent excess depletion from themother Serum and ionized magnesium also decline Serum phosphate levels are unchanged o Renal threshold for inorganic phosphate excretion is elevated in pregnancy due to increased calcitonin Iodine requirements increase due to three reasons o Maternal thyroxine production increases to maintain maternal euthyroidism and to transfer thyroid hormone to the fetus early o Thyroid hormone increases during the second half of the pregnancy o Primary route of iodine excretion is through the kidney