Cardiovascular Changes During Pregnancy

• Cardiovascular changes during pregnancy will be discussed
• This includes normal cardiac function, changes in pregnancy, and clinical relevance

Cardiovascular Function

• Arterial oxygen delivery (DO2) is equal to cardiac output multiplied by arterial oxygen content
• DO2 = CO x CaO2
• Cardiac output is influenced by heart rate and stroke volume
• Heart rate is influenced by nerves and hormones
• Stroke volume is influenced by blood volume and vascular resistance

Physiology

• Cardiovascular physiology functions to supply metabolic demand and ensure adequate cardiac output
• Cardiovascular physiology functions in conjunction with the arterial system

Pregnancy

• The placenta, a neuroendocrine organ, promotes maternal adaptations to meet the demands of both the mother and the fetus
• Adaptations include uteroplacental circulation
• Physiological changes that occur include those in the:
  • Respiratory system
  • Maternal-placental-fetal unit
  • Organ systems
  • Reproductive system

Neurohormonal Changes

• Neurohormonal changes in pregnancy lead to an increase in progesterone, estrogen, and relaxin
• These hormonal changes promote vasodilation of the systemic vasculature resulting in a 50% increase in renal blood flow (RBF) and glomerular filtration rate (GFR)
• Net sodium excretion increases and relative hypovolemia occurs
• Neurohormonal changes results in sodium and fluid retention

Plasma Volume

• Plasma volume increases during pregnancy which increases preload
• Dilutional anemia arises, and there is a reduction in oncotic pressure

Cardiac Output

• Increased preload and reduced afterload occur
• There is little change in contractility within the heart

Cardiac Output and Pregnancy

• Cardiac output increases
• The increase in CO is largely driven by an increase in stroke volume up to the second trimester
• Heart rate increases in the third trimester, and can increase up to 20%

Peripheral Vascular Resistance and Pregnancy

• Peripheral vascular resistance (PVR) decreases by 40%
• PVR peaks in the second trimester, then approaches baseline levels in the third trimester.

Blood Pressure and Pregnancy

• Overall decrease in blood pressure occurs during pregnancy
• There is an early decrease in the first trimester, with a peak decrease in the second trimester
• Blood pressure returns to baseline levels in the third trimester

Cardiac Remodeling

• Cardiac remodeling occurs during pregnancy

Vascular Remodeling

• Vascular remodeling occurs during pregnancy

Hemodynamic Summary

• The following all initially increase:

  • CO (cardiac output)
  • HR (heart rate)
  • Plasma Volume
  • RBC mass
  • LV wall mass

• SVR (systemic vascular resistance) decreases.

• BP (blood pressure) decreases.

Clinical Implications: Diagnosing Heart Failure

• Clinical implications for diagnosing heart failure include:
  • Increased shortness of breath on exertion/dyspnea, increased fatigue
  • Maximal cardiac output induced by exercise is achieved at a lower level of work
  • Maternal oxygen uptake is significantly increased compared to non-pregnant state
  • Resting minute ventilation, tidal volume increase, expiratory reserve volume, and functional residual capacity decrease
  • Mild 4-chamber dilation of the heart
  • Increased maternal heart rate occurs, an ejection systolic flow murmur appears and a third heart sound can be heard
  • Gestation dependent edema found in up to 80% of healthy pregnant women

Clinical Implications: ECG Abnormalities

• ECG abnormalities can occur during pregnancy

Echocardiography

• Echocardiographic findings in pregnant women may include mild dilatation of the left ventricle (LV) and right ventricle (RV), as well as the atria
• Systolic function is preserved
• Minimal mitral regurgitation, tricuspid regurgitation, and pulmonary regurgitation can occur
• Elevated filling pressures are present

The Placenta's Role

• The placenta produces hormones, including:
  • hCG (Human Chorionic Gonadotropin)
  • HPL (human placental lactogen) or hCS (somotomammotropin)
  • Human placental growth hormone
  • Progesterone
  • Estrogen
  • Prolactin

Adaptions to Accommodate Growing Baby

• Adaptions to accomodate a growing baby include:
  • Increased blood volume
  • Increased cardiac output
  • Increased oxygen needs
  • Increased protein and nutrient needs
  • A baby weighing 3kg
  • A placenta weighing 500g
  • Maternal weight gain
  • Musculo-skeletal changes
  • Reproductive organ changes

Respiratory System Changes

• Enlargement of the Uterus occurs
• The diaphragm rises 4cm
• Functional residual reserve decreases by 20%
• To compensate:
• The Subcostal angel widens
• The diameter of the thoracic cage increases
• The diaphragm functions normally
• Tidal volume increases (30-40%)
• Breathing becomes deeper
• The respiratory rate remains normal
• More CO2 is breathed out, and blood Ph increases slightly to 7.4

Hematological System Changes

• Arterial vasodilation and aldosterone occur
• Volume retention occurs
• Blood volume increases 30-40% (1.5l)
• Plasma volume increases 40-50%
• Red cell mass increases 18%
• Plasma volume increases more than red blood cell mass
• This results in a dilution effect where hemoglobin decreases from 13.3g/dl to 11g/dl
• Red blood cell morphology remains the same

Haematological Changes

• Pregnancy is a relative state of hypercoagulation
• Hypercoagulation prepares the body for delivery and prevents haemorrhage (bleeding)
• Clotting factors change
  • Factor 1: Fibrinogen increases by 50%
  • Factors II, V, VII, VWF, IX, X, XII increase (majority)
  • Fibrinolysis is reduced
  • Protein S decreases
  • Risk for deep vein thrombosis increases
• Leucocytes (white cell count) increase

Renal System Changes

• Enlargement of the Kidneys occurs, increasing to:
  • 10mm longer
  • 30% increase in volume
• Ureters become larger, decreasing peristalsis
• Renal plasma flow increases
  • The Glomerular filtration rate (GFR) increases 50%
  • Creatinine clearance increases
• Water and Salt Nitrogen metabolism changes
  • Water retention increases up to 6.5litres
  • Sodium net increase (fetus, plasma, maternal fluid status) occurs
  • High GFR
  • Increased sodium retention due to high aldosterone and estrogen
  • Increased reabsorption of sodium and water
  • Increase in potassium
  • Proximal tubular reabsorption increases
• Nitrogen metabolism changes:
  • GFR increases
  • Blood urea nitrogen decreases (25%)
  • Serum creatinine decreases

Other Renal Changes

• Renal tubular function changes
• High GFR occurs
• Glucosuria becomes more common
  • Check blood glucose level
• Proteinuria can occur but must be less than < 300mg/24 hours
• Need to drink more water
• The bladder becomes full
• The need to get up more often at night increases
• Risk for urinary tract infection increases

Liver Changes

• The size and histology of the liver remain the same
• Biochemical changes initiate by the liver
  • Fibrinogen increases (clotting factor)
  • Binding proteins (thyroid binding globulin) increase
  • Serum albumin levels decrease
• Normal physiological changes that can be confused with liver disease:
  • Spider angiomata
  • Palmar erythema
  • Decreased serum albumin level
  • Increase in ALP activity (mainly from placenta)
  • Increase in serum cholesterol
• Bile changes:
  • Residual volume increases
  • Emptying of the bile is delayed
  • Biliary cholesterol increases
  • Gallstones risk increases

Gastro Intestinal System Changes

• Gums become more vascular and softer, but there is no increase in gum disease
• Nausea occurs
  • Mostly in the first trimester
  • Corresponds with rapid increase in BHCG
• The GIT system relaxes
• Heartburn incidence increases
  • Delayed stomach emptying
  • Oesophageal tone decreases, lower pressure
  • Gastric pressure is higher
  • Gastro oesophageal reflux occurs
• Intestinal mobility decreases to allow for better absorption
  • The incidence of constipation increases
  • heamorrhoids occur

Metabolic Changes

• Glucose changes:
  • A diabetogenic state occurs
  • Human placental lactogen is present
  • Glucose is released
  • Insulin resistance increases (decreased uptake)
  • Glucose is needed for foetal growth and metabolism
  • To compensate glucose
  • insulin levels increase
  • Glucose levels remain normal in pregnancy
• Fat metabolism changes:
  • Plasma lipids increase
  • Free fatty acids increase
  • Cholesterol increases
• Metabolic rate increases:
  • Oxygen consumption increases (20%)
  • Tidal volume of breathing increases
  • Organ function increases

Iron and Folate Metabolism

• Iron demand increases (total demand during pregnancy):
  • Maternal demand increases in red blood cell mass (1000mg total during pregnancy)
  • Foetal need (300mg total during pregnancy)
  • Placental demands
• Iron binds to transferrin after absorption to be carried to liver, spleen, bone marrow, haemoglobin, and myoglobin
• Iron stored in ferritin
• Iron is actively transported trans placentally
• If iron levels are too low, there is a rise in risk of maternal anaemia -Iron must be supplemented in pregnancy with a healthy diet -50mg of ferri-iron tablet daily
• The need for Folate increases for foetal development and increase in red blood cell production
  • 5mg per day supplement

Other: Skin, Hair and Skeletal Changes

• Increase of oestrogen, vasodilation, and blood vessel proliferation in skin and hair -Improvement in Better facial skin, less acne -Spider angiomata occurs in 10-60% of people -Palmar erythema -Hyperpigmentation occurs (melanocyte stimulating hormone)
• Striae gravidarum (stretch marks, abdominal sides as pregnancy progresses)
• Hair changes occur
• All of the hair follicle cycle changes
• Scalp hair may increase (seldom decrease)
• Postpartum increases hair loss (but improves later)

Other: Breast Changes

• Breast enlargement occurs, as early as 8 weeks
  • Breast volume increases +_ 200ml/ breast
  • Areolae enlarge
  • White fluid may trickle down nipples (colostrum) in the second half of pregnancy
  • Breasts Prepare for lactation (breastfeeding)

Other: Skeletal Changes

• Change in balance occurs with growing uterus
• Lumbar lordosis occurs
• Relaxation of ligaments (relaxin hormone)
• Widening of Pubic symphysis (4.1mm to 7.7mm)

Body Weight Changes

• The mother experiences
  • Larger organs
  • More fluid retention
  • Blood volume increases
  • On average, weight increases 12.5kg in a normal healthy woman
  • 8kg is gained during last 20 weeks
  • 0.5kg is gained per week from 20 weeks gestation

The Reproductive System

• Ovaries change:
  • Enlargement of the Ovaries
  • The Corpus luteum of pregnancy becomes main source of progesterone up to 7 weeks
  • After 7 weeks the placenta mostly takes over progesterone production
  • Ovaries produces relaxin (change in ligaments)
• Fallopian tubes change:
  • Fallopian tubes become more vascular, water retention and enlarge

Uterus Changes

• Blood flow increases as the size of arteries and veins
• Trophoblast invades spiral arteries
• Blood flow = 600ml per minute at term
• The size of the Uterus moves from 50grams to 950grams

Uterus: Muscle Fibers

• Myometrial fibers grow 15 times
• There are 3 muscle layers
• The muscle fibers contract and relax
• Power during labour:
  • Contractions 2 minutes, intrauterine pressure
  • Contractions up to 50mmHg
  • Relaxation to allow for blood flow into placenta

Uterus: Components

• Components of the uterus change
  • Myometrial thickness increases
  • After 20 weeks, the uterus stretches
  • 10mm thick near term
• Isthmus/ Lower segment
  • The Isthmus softens and broadens
  • It is Dilated by growth of foetus
  • Almost no contractile tissue is present
  • muscle tissue
  • Cervix

Pelvic Floor and Vagina Changes

• The muscles and connective tissure Lengthen and soften
• The Vagina:
  • Becomes longer, more vascular
  • The Vagina epithelium thickens
  • Ph decreases (risk of candida)
• The Cervix:
  • Becomes more vascular, larger
  • Connective tissue softens
  • Glandular function increases
  • Mucous plug is present

Conclusion

• Pregnancy is a true example of physiological adaption
• Pregnancy is a complex process
• In cases of maladaptation or in patients with existing medical disorders pregnancy will be high risk

Renin-Angiotensin-Aldosterone System

• The renin-angiotensin-aldosterone system is activated in pregnancy
• This results in an early plasma volume increase
• Oestrogen mediates an increase in angiotensinogen
• Relaxin induces vasopressin release

Blood Pressure Changes

• All pressures are reduced early in pregnancy

Vasodilation

• Vasodilation occurs early in pregnancy
• This is driven by oestrogen, progesterone, and relaxin
• Vasodilation includes the kidneys
• A resultant decrease in PVR arises.
• Early normalization occurs

Plasma Volume and Red Cell Mass

• Total blood volume increases by 45-50%
• Red cell mass increases by 40%
• This results in dilutional anaemia

Remodeling

• LV mass increases by 50%
• Aortic stiffness decreases
• The left atrium (LA) and left ventricle (LV) enlarge
• Mild functional mitral regurgitation (MR) is possible
• Aortic regurgitation (AR) is not

Imaging Correlations

• Imaging may show a dilated LV
• Systolic function is normal
• 4-chamber enlargement is observed
• Transvalvular flow velocity increases
• Increased LV mass can be seen on imaging

Labour and Delivery

• Second major increase in cardiac output occurs during labour and delivery
• Prelabour CO is increased by 60-80%
• Abrupt increase in venous return occurs
• This continues for 72 hours postpartum

Clinical Correlations

• Common clinical findings include:
  • Resting tachycardia
  • Pedal oedema
  • Apex marginally displaced
  • Collapsing pulse
  • Ejection systolic flow murmur
  • An S3 heart sound can be normal
  • Dyspnoea

Puerperium

• Resolution of pregnancy-related changes is rapid
• Normalization occurs within 2 weeks
• Caution is needed in the first 24-72 hours due to increased venous return

Overall Conclusion

• A basic haemodynamic understanding is key to understanding haemodynamic changes during pregnancy
• Significant early changes occur
• Pregnancy impacts clinical evaluation
• Labour is a second stress test
• Rapid resolution occurs in the puerperium
• The impact of these changes may have on pathology