PHYSIOLOGY OF PREGNANCY

Objectives

􀂓 Symptoms and physical findings of each organ system 􀂓 Physiologic versus pathologic changes 􀂓 Diagnostic tests and interpretations during physiological changes

Symptoms of Pregnancy

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Nausea (1st TM)

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Breast and nipple tenderness (1st TM)

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Marked fatigue (1st & 3rd TM)

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Urinary frequency (1st & 3rd TM)

Breast Changes

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Early in pregnancy, tenderness and tightness is common

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After 8 weeks, breasts grow and blood vessels often are visible

 Nipples become larger and darker  A thick yellowish fluid can be expressed from the nipple

Pregnancy Tests are Very Reliable

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Turn positive at about the first missed period (4 weeks after the LMP or 14 days after conception.

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Detect ~30 units of HCG

Genital Tract

Increased vascularity and hyperemia 􀂓 Vagina 􀂓 Perineum 􀂓 Vulva Increased secretions Characteristic violet color of the vagina 􀂓 Chadwick’s sign Increased length to the vaginal wall Hypertrophy of the papillae of the vaginal mucosa

Uterus & Uterine Ligaments

The non-pregnant uterus weighs 70 grams. It is the size of a pear and can hold approximately two teaspoons of fluid. In pregnancy, the uterus grows to a weight of about 1 kg at term and has a capacity of approximately 7.5-12.5 L.

It enlarges through the stretching of muscle fiber to the size of a watermelon. The muscle fibers lengthen 7-11 times and widen 2-7 times. It also increases the number and size of its blood vessels and nerves.

Uterine blood flow

􀂓 Uterine blood flow is Increased 100 ml/min to 1200 ml/min This is the maximum capacity of the uterine circulation There is limited autoregulation When maternal Cardiac output declines, blood flow is shifted away from the uteroplacental circulation to the maternal brain, kidney and heart.

Braxton-Hicks contractions

After the first trimester (first 13 weeks of pregnancy), the uterus shows Braxton-Hicks contractions. They are: prelabor contractions that work toward shortening and widening the cervix and stretching the bottom of the uterus do not increase in length, frequency, or the intensity associated with labor usually are not painful but can be uncomfortable Benefit is to increase blood flow to the fetus

The

uterine ligaments

hold the uterus in place and undergo prolonged stretching during pregnancy. The

round ligaments

attach the uterus to the pubic bone in the front and help maintain the uterus in the center of the pelvis. Either a sharp pain or a dull ache near the hip joint is common when they are stretched upward. The

Uterosacral ligaments

connect the uterus to the sacrum and are often involved in backaches during pregnancy. Pain in the low back is the result of weak abdominal muscles, poor posture, and the weight of the abdomen pulling on the back ligaments

Cervix

 Becomes softer  Has more blood supply  Forms a mucus plug  Becomes about 12 X weaker by term (dec Collagen and Inc edema)

Genital Tract

􀂓 Uterine enlargement can compress IVC 􀂓 Can result in fall in venous return 􀂓 Furthermore a fall in CO 􀂓 peripheral resistance must increase to minimize fall in blood pressure 􀂓 As SPR is low in pregnancy, Supine hypotensive syndrome can occur 􀂓 relieved with position advice

Organ systems

Metabolic Changes 􀂓 Cardiovascular system 􀂓 Pulmonary system 􀂓 Urinary system 􀂓 Endocrine system 􀂓 Gastrointestinal Tract 􀂓 Skin

Weight Gain (average 12.5kg)

Water Metabolism

 Increased water retention  Osmolality decrease 10 mOsm/kg  Extra water gain: 6.5 L

Carbohydrate Metabolism

 Fasting glucose (-)  PP glucose (+), insulin (+)  Insulin resistance (+)  Ketonemia

Hematological Changes

Blood Volume

 Increase 40~45%  Mild anemia, but should not below 11 g/dl

Physiologic anemia of pregnancy 􀂓

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Physiologic intravascular change

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Plasma volume increases 50-70 % Beginning by the 6th wk

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RBC mass increases 20-35 %, Beginning by the 12th wk

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Disproportionate increase in plasma volume over RBC volume--- Hemodilution ------- fall in the hemoglobin and hematocrit readings

Iron deficiency anemia

 With erythropoiesis of pregnancy, iron requirements increase.

 Required amounts of iron may not be available from body stores or diet  Supplementation is recommended  At term, Hemoglobin less than 10.0 is due to iron deficiency

White Blood cells

 Increase in WBC count (mainly neutrophils)  WBC count up to 15,000 may be due to pregnancy  Problem interpreting infection  Further increase in labor and early puerperium 

Coagulation

 Activated state  Coagulation tests show hypercoagulable state (BT, PT, APTT, Fibronogen)  Fibrinogen: 300 mg/dl  450 mg/dl  D-dimer increase  Platelet decrease due to hemodilution  Define thrombocytopenia: < 116,000

Cardiovascular system

Cardiac output

Begins to increase by the 5th wk Rise of 40 % by 20-24 wks Increased both HR and SV The notable increase in plasma volume or preload contributes to the increase SV As pregnancy advances to term, the HR continues to increase but the SV falls to close to normal levels, Relief of excess cardiac load near term

Interpretation of tests during pregnancy

Echocardiogram 􀂓 Increased left ventricular wall mass 􀂓 􀂓 Increased end diastolic dimensions Increase in EDV and therefore inc in SV Electrocardiogram 􀂓 Slight left axis deviation

Respiratory system

Respiratory Changes

 Respiratory capacity increases  Shortness of breath  Pulmonary reserve decreases  Increased risk of muscle soreness  Tendency to hyperventilate

RESULT

adjust the intensity level and duration of exercise

Respiratory system

Mechanical 􀂓 diaphragm Consumption 􀂓 Increase in needed oxygen Stimulation 􀂓 Progesterone stimulation

Respiratory

Mechanical 􀂓 Diaphragm rises 4 cm 􀂓 Less negative intrathoracic pressure 􀂓 Dec RV-Residual Volume (volume after max expiration) 􀂓 No impairments in diaphragmatic or thoracic muscle motion 􀂓 Lung compliance remains unaffected

Respiratory

Consumption 􀂓 O2 consumption Increases 15-20 % 􀂓 50 % of this increase is required by the uterus 􀂓 Despite increase in oxygen requirements, with the increase in Cardiac Output and increase in alveolar ventilation oxygen consumption exceeds the requirements.

􀂓 Therefore, arteriovenous oxygen difference falls and arterial PCO2 falls

Respiratory

Stimulation 􀂓 Progesterone is known to directly stimulate ventilation 􀂓 Progesterone increases the sensitivity of the respiratory centers to CO2 􀂓 Also, it is thought to reduce total pulmonary resistance

Physiologic changes

Increased desire to breathe 􀂓 70 % of pregnant women experience this.

􀂓 Occurs during 1st trimester without mechanical factors 􀂓 The lower PCO2 then paradoxically causes dyspnea

Urinary Changes

 Kidneys grow and filter more blood as the blood volume increases  Become more susceptible to bladder and kidney infections  Bladder becomes compressed causing frequent urination and incontinence

Urinary System-Dilation

Calyces, renal pelves, and ureters undergo marked dilatation More prominent on the right Partial obstruction of the ureters can occur at the pelvic brim Progesterone produces smooth muscle relaxation

Urinary System-inc GFR

GFR and renal plasma flow increases 40 % by mid-gestation Plateaus, then remains unchanged until term Elevated GFR causes a decrease in serum levels of creatinine and blood urea nitrogen NL GFR 120-160 ml/min

Urinary System-Proteinuria

Normally not evident Average is 115 mg/day-260 mg/day Therefore, our 300 mg screen would exceed most normal variations

Endocrine

Endocrine Pancreas

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Postprandial hyperglycemia To ensure sustained glucose levels for fetus Accelerated starvation Early switch from glucose to lipids for fuels Insulin resistance promotes hyperglycemia Resistance-Reduced peripheral uptake of glucose for a given dose of insulin Mild fasting hypoglycemia occurs with elevated FFA, triglycerides,and cholesterol

Insulin resistance

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Anti-insulin environment is aided by: placental lactogen Like growth hormone Increases lipolysis and FFA Increases tissue resistance to insulin Increased unbound cortisol Estrogen and Progesterone may also exert some anti-insulin effects

Thyroid

   

Estrogen stimulates Increase in TBG Total T3 and T4 are increased However the active hormones remains unchanged hCG stimulates thyroid TSH is reduced Iodine deficient state Due to Increased renal clearance To rule out pathologic changes Early in pregnancy TSH can be used Later free T4 is needed

Pituitary Changes

 Enlargement (Prolactin Increase)  Problem if there is a prolactinoma

Digestive Changes

 Digestive system slows  Intestines are pushed up and to the sides  Smooth muscle of the stomach relaxes and can cause heartburn 

Constipation and hemorrhoids are common during pregnancy



Morning sickness

Gastrointestinal Tract

Displacement of the stomach and intestines Appendix can be displaced to reach the right flank Gastric emptying and intestinal transit times are delayed ( hormonal and mechanical factors) Vascular swelling of the gums

Liver

Liver morphology unchanged Alkaline phosphatase doubles GGT and bilirubin are slightly lower Decreased plasma albumin

Gallbladder

Impaired contraction High residual volumes Promotion of stasis Stasis associated with increased cholesterol saturation of pregnancy, supports predisposition of stones Intrahepatic cholestasis Retained bile salts-pruritus gravidarum

Skin changes

Striae gravidarum Linea nigra Chloasma Spider angioma, palmar erythema (estrogen)

Skin

Melasma

More common in dark skin people More pronounced in the summer Fades a few months after delivery Repeated pregnancy can intensify Can occur in normal non-pregnant

Striae

Reddish slightly depressed Breasts, thighs, and abdomen In future pregnancies they appear as glistening, silver lines

Hyperpigmentation

Melasma and linea nigra Estrogen and progesterone Some melanocyte stimulating effect