Maternal physiology Sindhu Srinivas, md, msce division of Maternal Fetal Medicine Goals
Date 08.07.2017 Size 25.56 Kb. #24953
Sindhu Srinivas, MD, MSCE Division of Maternal Fetal Medicine Goals To understand the normal changes associated with pregnancy Body Water TBW increases from 6.5L to 8.5L At term water content of fetus, placenta and AF is 3.5L BV, PV, RBC, extravascular, intracellular Pregnancy is a condition of chronic volume overload Water retention exceeds Na retention-decreased plasma osmolality (Na dec by 3-4) To recognize physiologic and pathologic states during pregnancy Hematology – Blood volume Increases progressively from 6 to 8 weeks’ gestation maximum volume at 32 weeks - 45% increase possibly due to estrogen stimulation of renin-angiotensin-aldosterone system (Inc Prog, NO->Dec SVR->Dec MAP->Inc Na retention) Hematology – RBC mass Red blood cell mass increases by 250-450 cc by term Increased production Possibly hormonally mediated Hematology - Iron Maternal requirement is 1000mg normal pregnant woman needs to absorb about 3.5 mg/day of iron the goal of iron supplementation is to prevent maternal iron deficiency iron is actively transported to the fetus Hematologic changes IMPLICATIONS The increase in plasma volume and rbc mass translates into a 45% increase in circulating blood volume may protect from hemodynamic instability may serve to dissipate fetal heat production and provide increase renal filtration physiologic anemia of pregnancy may function to decrease blood viscosity may improve intervillous perfusion? Hematology LEUKOCYTES Peripheral wbc rises progressively during pregnancy 1st ∆ – mean 9500/mm3 (3000-15,000) 2nd and 3rd ∆ – mean 10,500 (6000-16,000) Labor – may rise to 20-30,000 Rise is due to increase in pmns (demargination) PLATELETS Platelets experience a progressive decline but should remain within normal range Likely due to increased destruction Hematology COAGULATION FACTORS Increased levels Fibrinogen (Factor I) Factors VII through X No change in prothrombin (Factor II), Factors V and XII Decline in platelet count, Factors XI and XIII Bleeding time and clotting time are unchanged in normal pregnancy Maternal cardiac output increases about 30-50% during pregnancy (mean 33%) pregnancy maximum of 6 L/min CO remains maximal until delivery Earliest rise in CO is due to increase in SV As pregnancy progresses Gradual increase in mat HR (15-20 bpm rise) SV declines to near non-pregnant levels increase HR is what maintains the elevated CO Cardiovascular – Cardiac output CO is position dependent Lower when supine IVC compression by the uterus reduces venous return to the heart At 38-40 weeks, there is a 25-30% fall in CO when turning from the side to the back Fall in CO is compensated by a rise in peripheral vascular resistance supine hypotensive syndrome (1-10% patients) Cardiovascular – Cardiac output Distribution of CO First trimester and non-pregnant state By term Uterus receives 17% Breasts 2% Reduction of the fraction of CO going to the splanchnic bed and skeletal muscle CO to the kidneys, skin, brain and coronary arteries does not change Cardiovascular – Arterial BP BP varies with position Peripheral vascular resistance falls during pregnancy Progesterone’s smooth muscle relaxing effect ?heat production by the fetus vasodilatation The reduction in PVR may lead to a progressive fall in systemic arterial bp during the first 24 weeks of pregnancy Gradual rise after 24 weeks non-pregnant levels by term Cardiovascular – Venous system Venous compliance increases during pregnancy decrease in flow velocity and stasis ?progesterone effects on smooth muscle Forearm venous pressure increases by 40-50% Calf venous pressures are always higher due to the enlarging uterus Cardiovascular - LV function Left ventricular dimensions and volume increase during pregnancy most parameters of LVF are the same as in the non-pregnant state Ejection fraction, rate of internal diameter shortening, percentage of fractional shortening, and ventricular wall thickness Bottom line: preservation of myocardial function Signs and Symptoms of Normal Pregnancy Symptoms reduced exercise tolerance dyspnea Signs peripheral edema distended neck veins point of maximal impulse displaced to the left Signs and Symptoms of Normal Pregnancy Auscultation increased splitting of the first and second heart sound S3 gallop SEM along the left sternal border Continuous murmurs Signs and Symptoms of Normal Pregnancy CXR straightening of left heart border heart position more horizontal – may appear as cardiomegaly on cxr increased vascular markings in lungs ECG left axis deviation non-specific ST-T wave changes Cardiovascular - Labor First stage of labor: 12-31% rise on CO due to an increase in SV Second stage of labor: 34% increase in CO Not only pain-related UCs result in the transfer of 300-500 cc of blood from the uterus to the general circulation Enhanced venous return to the heart Increase in CO by 10-15% Cardiovascular - Postpartum Immediate pp period: 10-20% rise in CO release of obstruction of venous return extracellular fluid mobilization Rise in CO associated with reflex bradycardia SV increases this may persist for one to two weeks after delivery QUESTION During which of the following states is the blood pressure lowest? First trimester Second trimester Third trimester Non pregnant QUESTION Increased cardiac output immediately postpartum is due to: Increased HR Release of obstruction of venous return Reduced mobilization of extracellular fluid Reduced stroke volume Respiratory system UPPER RESPIRATORY TRACT Hyperemic mucosa of nasopharynx Estrogen-mediated nasal stuffiness and epistaxis Polyposis of nose and sinuses may occur and regress after delivery “chronic cold” MECHANICAL CHANGES Configuration of thoracic cage changes early in pregnancy Increase in subcostal angle, transverse diameter and circumference of chest With advancing gestation, the level of diaphragm is pushed up Changes in pulmonary function tests during pregnancy Serial measurements of lung volume compartments during pregnancy. Functional residual capacity decreases approximately 20 percent during the latter half of pregnancy, due to a decrease in both expiratory reserve volume and residual volume. Redrawn from Prowse, CM, Gaensler, EA, Anesthesiology 1965; 26:381. Serial measurements of lung volume compartments during pregnancy. Functional residual capacity decreases approximately 20 percent during the latter half of pregnancy, due to a decrease in both expiratory reserve volume and residual volume. Redrawn from Prowse, CM, Gaensler, EA, Anesthesiology 1965; 26:381. Respiratory system LUNG VOLUME AND PULMONARY FUNCTION 30-40% increase in tidal volume (Amount of air I and E with each breath) 30-40% increase in minute ventilation (likely P4 mediated) ERV falls by 20% Vital capacity and inspiratory reserve volume remain unchanged Respiratory system LUNG VOLUME AND PULMONARY FUNCTION Respiratory rate is unchanged Due to elevation of the diaphragm Total lung volume decreases (diaphragm) by 5% Residual volume decreases (RV) by 20% FRC is reduced 20% No change in FEV1 or the ratio of FEV1 to forced vital capacity Respiratory system GAS EXCHANGE Minute ventilation rises 30-40% by late pregnancy O2 consumption increases only 15-29% Results in higher PAO2 (alveolar) and PaO2 (arterial) Normal PaO2: 104-108 mmHg Fall in PACO2 and PaCO2 levels Normal PaCO2 level: 27-32 mmHg Increases gradient of CO2 facilitating transfer from fetus to mother Arterial pH remains unchanged Increased bicarbonate excretion via kidneys Respiratory system DYSPNEA OF PREGNANCY Common complaint 60-70% of patients late first or early second trimester Likely due to various factors reduced PaCO2 levels awareness of increased tidal volume of pregnancy QUESTION Which of the following is increased in pregnancy? Renal system ANATOMY Kidney enlargement increased renal vascular and interstitial volume, R>L Ureteral and renal pelvis dilatation by 8 weeks Right > left mechanical compression by uterus and ovarian venous plexus smooth muscle relaxation by progesterone Implications Increased incidence of pyelonephritis difficulty in interpreting radiographs interference with studies Renal system RENAL HEMODYNAMICS Effective renal plasma flow (ERPF) and GFR increase Filtration fraction falls Returns to normal by late third Δ Endogenous creatinine clearance increases Renal system METABOLITES increased GFR decline in serum urea and creatinine BUN – 8-9 mg/dl by end 1st Δ Decline in serum creatinine 0.7 mg/dl by end 1st Δ 0.5-0.6 mg/dl by term Early decline in serum uric acid levels nadir at 24 weeks same as nonpregnant level at end of pregnancy due to increased reabsorption of urate Renal system SALT AND WATER METABOLISM Plasma osmolality begins to decline by 2 weeks after conception reduction in serum sodium and other anions Sodium loss during pregnancy 50% rise in GFR Progesterone: natriuresis Renal tubular reabsorption of Na+ increases (aldosterone, estrogen and deoxycorticosterone) Sodium homeostasis Renal system NUTRIENT EXCRETION Increase in glucose excretion 1-10 g glucose excretion per day Due to 50% increase in GFR implications Increase in amino acid excretion during gestation no increased protein loss (100-300 mg/24 hr) Increased urinary loss of folate and vitamin B12 QUESTION All of the following are increased in pregnancy except: Renal plasma flow GFR Serum creatinine Tubular sodium resorption Gastrointestinal - Appetite Increase early 1st Δ Increase intake 200 kcal by end 1st Δ RDA: 300 kcal/day during pregnancy Sense of taste may be blunted Pica check for poor weight gain and refractory anemia South - clay or starch (laundry or cornstarch) UK – coal Also soap, toothpaste and ice pica Gastrointestinal - Mouth Unchanged pH or production of saliva Saliva production is unaltered Ptyalism – usually in women with HEG due to inability to swallow Can lose up to 1-2 L of saliva per day Decreasing starchy foods might help Gums – edematous and soft Epulis gravidarum regress 1-2 mos after delivery excise if persistent or excessive bleeding Gastrointestinal - Stomach Decreased tone and motility progesterone possibly due to decreased levels of motility Conflicting info about delayed gastric emptying Reduced tone of the gastroesophageal junction sphincter Increased intraabdominal pressure leads to acid reflux Lower incidence of PUD may be due to decreased gastric acid secretion delayed emptying, increase in gastric mucus, and protection of mucosa by prostaglandins Reduced motility of small bowel increased transit time in the third trimester and postpartum Enhanced iron absorption as a response to increased iron needs Gastrointestinal - Colon Constipation Mechanical obstruction by the uterus Reduced motility (p4) Increased water absorption Portal venous pressure is increased Dilation of gastroesophageal vessels issue in those with preexisting esophageal varices Dilation of hemorrhoidal veins Gastrointestinal - Gallbladder Fasting and residual volumes double in 2nd and 3rd Δ Biliary cholesterol saturation increases and chenodeoxycholic acid decreases increased risk gallstone formation Gastrointestinal - Liver Liver does not enlarge Hepatic blood flow remains unchanged CO to the liver decreases by ~35% Spider angiomata and palmar erythema Lab data Drop in serum albumin Rise in serum alkaline phosphatase placental production and some hepatic production Rise in serum cholesterol, fibrinogen, ceruloplasmin, binding proteins for corticosteroids, sex steroids, thyroid hormones, and vitamin D No change in serum bilirubin, AST, ALT, protime and 5’ nucleotidase Rise in GGT is controversial Gastrointestinal system NAUSEA AND VOMITING Morning sickness complicates 70% of pregnancies Onset 4-8 weeks up to 14-16 weeks Cause? Relaxation of smooth muscle of stomach, elevated levels of steroids and hCG Rx – supportive: reassurance, support, and avoiding triggers… HEG weight loss, ketonemia, electrolyte imbalance and dehydration possible renal or hepatic damage IVF, antiemetics Conclusion Understanding maternal physiology is crucial in understanding the changes and clinical scenarios associated in pregnancy This knowledge will help us distinguish the physiologic and pathologic processes during pregnancy This knowledge will also improve patient’s education about their pregnancy Endocrine - Thyroid The normal pregnant woman is euthyroid Changes in thyroid morphology and lab indices Estrogen-induced increase in TBG Decreased circulating extrathyroidal iodide Thyroid enlargement usually not detected by exam Normal thyroidal uptake of iodide Serum TSH decreases early in gestation rises to pre-pregnancy levels by end of first Δ T4 increases early in gestation role of hCG stimulating the thyroid Rise in TBG leads to rise in total T4 and total T3 active hormones free T4 and free T3 are unchanged Free T4 is the most reliable method of evaluating thyroid function in pregnancy Endocrine - Adrenal glands Expansion of the zona fasciculata site of glucocorticoid production Plasma corticosteroid-binding globulin (CBG) rises due to enhanced liver synthesis Free plasma cortisol rises increased production and delayed clearance Plasma DOC (deoxycorticosterone) rises DHEAS (dehydroepiandrosterone) decreases Testosterone is slightly elevated Increased SHBG and androstenedione Hypertrophy and hyperplasia of the B cells Fasting associated with accelerated starvation maternal hypoglycemia, hypoinsulinemia and hyperketonemia due to diffusion of glucose by the fetoplacental unit Feeding response hyperglycemia, hyperinsulinemia, hypertriglyceridemia and reduced tissue sensitivity to insulin glucose response greater during pregnancy peripheral resistance to insulin: diabetogenic effect of pregnancy . hPL and cortisol mediated greater insulin resistance as the pregnancy advances Endocrine - Pancreas Fetus primarily depends on glucose Facilitated diffusion carrier-mediated but not energy dependent process Active transport of amino acids to the fetus Ketones diffuse freely across the placenta Endocrine - Pituitary The pituitary gland enlarges in pregnancy proliferation of chromophobe cells on the anterior pituitary stalk remains midline Skin Spider angiomata (face, upper chest, and arm) and palmar erythema elevated estrogen levels both regress after delivery Striae gravidarum Increased eccrine sweating and sebum excretion Skin Hyperpigmentation Melasma: “mask of pregnancy” Nevi may darken, enlarge or show increased activity rapidly changing nevi should be excised Hairs in telogen phase decrease in late pregnancy increases after delivery hair loss 2-4 mos pp re-growth in 6-12 mos Masculinization of the skin rarely occurs evaluate for possible luteomas of pregnancy (which regress after delivery) Breasts Early change tenderness, tingling and heaviness vascular engorgement leads to enlargement Ductal growth due to e2 Alveolar hypertrophy due to p4 Enlargement and pigmentation of areolae Colostrum may be expressed later in pregnancy Milk production E2, p4, prolactin, hPL, cortisol and insulin Lactation likely due to drop in estrogen and progesterone after delivery Skeleton Lordosis keep center of gravity over the legs back pain… Relaxin relaxation of the pubic symphysis and sacroiliac joints facilitates vaginal delivery but may lead to discomfort Implications unsteadiness of gait and trauma from falls Skeleton Total serum calcium declines throughout pregnancy until 34-36 weeks due to the fall in serum albumin Serum ionized calcium is constant and unchanged “Physiologic hyperparathyroidism” increased gut absorption decreased renal losses no bone loss seen in bone density studies preservation due to calcitonin? Rate of bone turnover and remodeling increases throughout pregnancy Eye Increased thickness of cornea due to fluid retention (contact lens intolerance) Decreased intraocular pressure Share with your friends:
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