Physiologic Changes in Pregnancy

Physiologic Changes in Pregnancy
By:Thomas S. Ivester, MD, MPH
Maternal-Fetal Medicine

Relevance of OB physiology
* 5-10 % of women in ER are pregnant
o Many don’t know or show
* Any female of reproductive age could be pregnant
o Should be assumed so!
* Virtually every organ system affected
* Can touch almost any specialty

Case history
Case 1

* 36 y.o. female presents to ER
* CC: Fatigue, dyspnea, chest pain
* HPI:
o Progressive SOB and dyspnea over several weeks.
o Poor exercise tolerance and easy fatigability
+ ‘get winded after 1 flight of stairs’
o Substernal chest pain, peaks in morning and night
o Nocturnal cough, semi-productive – clear
o Leg swelling
o polyuria
* PMH
o Mild obesity
* Ob/gyn – menses at age 12; irregular menses; no pregnancies
* Meds
o Oral contraceptives
o multivitamins
* Social
o Married for 2 years. No exposures

Case 1: PE
* Skin
o warm, clammy. Mild facial acne and increased hair – medium coarseness
* HEENT
o NC/AT. Nasal mucosa slightly hyperemic.
o Mild non-nodular thyromegaly
* CV
o Tachycardia (HR 107)
o + JVD
o 2/6 systolic murmurs over pulmonic and aortic v.
* Chest
o Clear bilaterally. Diaphragm elevated with decreased excursion
* Ext
o 1+ pretibial pitting edema
* Abd
o Skin – spider angiomata and striae. Medium course hair, infraumbilical.
o Distended, firm, non-tender.

Studies / labs
* EKG:
o Sinus rhythm; tachy; Left axis deviation
* CXR:
o Lungs clear. Cardiomegaly. Increased vascular markings
* Labs:
o Hct 32% (low); WBC 12 (high)
o Cholesterol 300 mg/dl
o D-dimer elevated
o Potassium and creatinine low

What does she have???
General Principles
* Most changes begin early
o Even before pregnancy recognized
* Most are hormonally driven
o Progesterone, estrogen, renin / aldosterone, cortisol, insulin
o Some ‘mechanically’ driven
* Designed to optimize conditions for fetus & prepare for delivery
o Delivery of oxygen & nutrients
Cardiovascular & Hematologic
* Vascular
o Decreased tone / vaso-relaxation
+ SVR decreased 20%
o Positional effects
o Placenta – low resistance shunt
* Hematologic
o Blood volume increases 50-100%
o RBC increases 25-40%
+ Relative anemia (“physiologic”)

Hematologic
* Hypercoagulable
o Estrogen & Vascular stasis
o Increased risk for thromboembolic disease
+ Increase in fibrinogen, all coag factors except II, V, XII
+ Fall in protein S and sensitivity to APC
* Fall in platelets and factor XI and XIII
* Increase in WBC

Changes in the Pump
* Cardiac axis displaced cephalad and left
o PMI lateral & elevated (not just due to baby!)
+ Altered thoracic dimensions
o Left axis deviation
* Murmurs > 96%
o Virtually all valves
+ Esp. Aortic and Pulmonary
+ Mammary Souffle
* Rate – increased (80’s typical)
* Ventricular distention – 25% increase
* Rhythm
o Non-specific ST & T changes
o Increase in dysrhythmias
+ Physiologic hypokalemia
* Anatomy
o LVH & Pericardial effusion
* Function
o Increased & markedly fluctuating output

Blood Pressure
Pregnancy Adaptations
Anatomical considerations
Uterine Position over Time
Cardiac Output – Positional Effects
* Aorto-caval Compression
Labor Changes
* SVR – Increased 10-25% with CTX
* Volume – autotransfusion 300-500cc
* Cardiac output -
o <3cm Increased 17%
o 4-7cm Increased 23%
o >8cm Increased 34%
The Fetus and Placenta
* Fetus (aka – “the parasite”)
o A sensitive survivor
o A window
* Placenta
o A veritable hormone factory
o Receives 20-25% of cardiac output*
+ 750-1000 ml/min
+ Refractory to vasoactive meds
o Uses as much O2 as fetus

Normal physiology or disease?
Signs & Symptoms of Normal Pregnancy that may Mimic Heart Disease
* Signs
o Peripheral edema
o JVD
* Symptoms
o Reduced exercise tolerance
o Dyspnea
* Auscultation
o S3 gallop
o Systolic ejection murmur
* Chest x-ray
o Change in heart position & size
o Increased vascular markings
* EKG
o Nonspecific ST-T wave changes
o Axis deviation
o LVH
Other systems
Changes in the Filter
* Renin – stimulated by progesterone
o Also made by placenta
o Angiotensinogen Angiotensin I Angiotensin II Aldosterone Distal tubule
+ Net absorption of Na+
+ Excretion of K+
+ Water retention: 6-8 liters
* Increased renal blood flow
o 50-75% increase
o GFR – 50% increase
o Decreased Albumin = lower colloid oncotic pressure

Other urinary tract changes
* Ureteral dilation / hydroureter
o Smooth muscle relaxation
o Later exacerbation by uterine obstruction
o Urinary stasis*
* Dilation of pelves and calyces
* Increased kidney size
Lungs and respiration
Respiratory Adaptations
o No change in rate or IRV
o Thorax
+ Tr. Diameter 2cm; circumference 5-7cm
o Increased minute ventilation
o Reduced FRC – 20%
o Increased Tidal Volume – 30-40%
o Compensated respiratory alkalosis
+ pH 7.4+
+ PaO2; PaCO2 (40 – 30)
+ Drives gradient b/w mom and fetus

Respiratory Changes
Gastrointestinal
* Slowed GI motility
o Constipation, early satiety
* Relaxation of LES
o GERD
* Nausea / vomiting
o Often proportional to HCG level
* Liver / gallbladder
o Biliary stasis, cholesterol saturation
+ More stones
o Coagulation factors
o Increased binding proteins (thyroid, steroid, vitamin D)
Other “Adaptations”

* “I can’t see my feet!!!”
o Altered center of gravity
o Altered gait
o Greater joint laxity
+ Widening of symphysis pubis
+ Affects other joints
+ Thorax; widened costovertebral angle
o Fatigue / somnolence

Integumentary Changes
* Spider angiomata and palmar erythema
* Hair growth (abdomen and face)
* Mucosal hyperemia
* Striae gravidarum
* Hyperpigmentation (esp. linea nigra)
o Rashes and acne relatively common
Other Endocrine
* Pancreas
o Carbohydrate metabolism -Insulin resistance
+ Human placental lactogen, cortisol
* Thyroid Function
o Increased TIBG (via liver)
o Increased total T4 and T3
+ free levels unchanged
+ HCG suppresses TSH
* Adrenal function
o Free plasma cortisol is elevated
+ CRH from placenta stimulates ACTH
Immunology

* Must adapt to accept ‘allograft’
* Immune response altered, but not deficient
* Modulates away from cell-mediated cytotoxic effects
o Progesterone effect
o NK cells decrease by 30%
o Enhanced humoral / innate immunity
+ Immunoglobulins still active
+ IgG crosses placenta
o More susceptible to CMV, HSV, Varicella, Malaria
o Decrease in symptoms of some autoimmune disorders

Pregnancy – not a disease

* Profound changes in physiology and anatomy
* Affects most organ systems
* Can dramatically impact disease states, susceptibility, and treatment
* Almost all will encounter and treat pregnant women
o Even if you don’t know it
* Under-appreciation of changes will lead to suboptimal treatment or outright mistakes

Physiologic Changes in Pregnancy.ppt