1. Physiologic Changes in Pregnancy
Heather M. Said, DO
Assistant Professor, Maternal Fetal Medicine

2. Objective
Discuss changes in maternal physiology associated with pregnancy

3. Cardiovascular System

4. Cardiovascular System
Earliest and most dramatic changes of pregnancy
Goal to improve fetal oxygenation and nutrition

5. Cardiovascular System: Anatomic Changes
Heart displaced upward and to the left
Apex moved laterally and overall assumes more horizontal position
Result of diaphragmatic elevation from enlarging uterus
Increased ventricular muscle mass
Increased blood volume  increased size of left ventricle and left atrium
Clinical correlation
Above changes may be misinterpreted as pathologic on chest x-ray if pregnancy isn’t taken into account

6. Cardiovascular System: Functional Changes
Cardiac output increases 30-50%
Half of this increase occurs before 8 weeks gestation
Why the increase?
Remember cardiac output = stroke volume x heart rate
First half of pregnancy: Increased stroke volume
Increased SV from increased blood volume as early as 6-8 weeks
45% increase in blood volume (peak) by 32 weeks
Systemic vascular resistance decreases (progesterone)
Second half of pregnancy: Increased heart rate

7. Cardiovascular System: Functional Changes
Cardiac output begins to decrease later in pregnancy as enlarging uterus compresses vena cava and obstructs return of blood to heart
Worse in the supine position
10% will report dizziness, light headedness or syncope when supine too long
Also known as inferior vena cava syndrome
Clinical correlation
Reason why we advise pregnant patients to sleep on their side and reason why we use left lateral tilt during surgical procedures

8. Cardiovascular System: Functional Changes
Distribution of cardiac output changes with pregnancy
First trimester: Uterus receives 2% of CO
At term: Uterus receives up to 20% of CO
Clinical correlation: Hemorrhage potential!
Less flow to splanchnic bed and skeletal muscle in pregnancy

9. Cardiovascular System: Functional Changes
Changes in blood pressure
Decrease in blood pressure beginning at 7 weeks
Nadirs at weeks (decline of around 10 mm Hg)
BPs gradually return to pre-pregnancy values by term
Changes in heart rate
Pulse increases by bpm by end of pregnancy

10. Cardiovascular System: Functional Changes
Changes in labor
CO increases 40% with uterine contractions
MAP increases by 10 mm Hg
Epidural blunts these responses
 somewhat driven by pain
Changes immediately postpartum
Dramatic increase in CO after delivery
Venous return no longer impeded by the gravid uterus
Blood that was going to placenta/gravid uterus now redirected systemically
Highest cardiac output of all occurs during this phase
Clinical correlation: A patient with cardiac disease that does not tolerate excess volume well can decompensate postpartum

11. Cardiovascular System: Physical Findings
Increased S2 split with expiration
Distended neck veins
Low grade systolic ejection murmur
Increased blood flow across aortic and pulmonic valves
Diastolic murmurs are never considered normal in pregnancy

12. Cardiovascular System: Diagnostic Tests
Serial blood pressure assessment
Highest when seated
Lower if supine
Lowest when lying in lateral recumbent position
Chest x-ray
Enlarged cardiac silhouette
EKG
Left axis deviation

13. Respiratory System

14. Respiratory System
Fueled by increased oxygen demand of mother and fetus
Driven by progesterone

15. Respiratory System: Anatomic Changes
Diaphragm elevated 4 cm
Due to enlarging uterus
Subcostal angle widens
Increased chest diameter and circumference

16. Respiratory System: Functional Changes
20% increase in total body O2 consumption
50% consumed by uterus/placenta/fetus
30% by heart and kidneys
18% by respiratory muscles
Rest by mammary tissues

17. Respiratory System: Functional Changes
Decreased (d/t elevated diaphragm)
Residual volume (20%)
Functional residual capacity
Total lung volume (5%)
No Change
Respiratory rate
Increased
Tidal volume (30-40%)
Inspiratory capacity (5%)
Minute ventilation (30-40%)

18. Respiratory System: Functional Changes
Progesterone  increased chemoreceptor sensitivity to CO2
 Increased ventilation  reduced pCO2
 Respiratory alkalosis
 Renal compensation (increased renal excretion of bicarb)
Lower bicarb in pregnancy
Clinical correlation: Keep these acid base changes in mind when interpreting ABGs or bicarb values in pregnancy!

19. Respiratory System: Symptoms
Dyspnea is common in pregnancy
Likely physiologic response to low arterial pCO2
Be careful not to disregard all dyspnea as physiologic, however
Mucosal hyperemia
Nasal congestion

20. Respiratory System: Physical Findings
None

21. Respiratory System: Diagnostic Tests
CXR can show increased pulmonary vasculature d/t blood volume
ABGs show compensated respiratory alkalosis
Arterial pCO2
Non-gravid: mm Hg
Gravid: mm Hg
Bicarb
Non-gravid: mEq/L
Gravid: mEq/L
Arterial pH
Non-gravid:
Gravid:
This is a very important concept in evaluating a pregnant patient with an asthma exacerbation or DKA, etc! A pH of 7.35 is NOT normal in pregnancy and is highly concerning!

22. Hematologic System

23. Hematologic System Intentions
Maximize O2 carrying capacity of the mother
 Enhanced oxygen delivery to the fetus
Minimize effects of impaired venous return
Minimize effects of blood loss from delivery

24. Hematologic System: Anatomic Changes
Primary changes
Increased plasma volume
Peaks around weeks (50%)
Increased red cell volume
Increases 450 mL
Not as much as plasma volume increase
 dilutional anemia of pregnancy
Increased coagulation factors
Increased hepatic production
Estrogen driven

25. Hematologic System: Anatomic Changes
Increased iron needs in pregnancy
1000 mg additional iron to prevent maternal anemia
Actively transported to fetus
Fetal levels maintained despite maternal levels
Decreased hemoglobin
Nadir around g/dL
Increased WBC counts
Especially during labor
Demargination
Slightly decreased platelet counts
k by third trimester

26. Hematologic System: Anatomic Changes
Clotting factors
Increased: Fibrinogen (factor I), fibrin split products, factors VII, VIII, IX and X
Unchanged: Prothrombin (factor II), factors V, XII
Decreased: Protein C and S (natural anticoagulants)
Net effect is hypercoagulable state

27. Hematologic System: Functional Changes
RBC alterations allow
Enhanced oxygen uptake in lungs (Hgb O2 affinity)
Improved delivery of O2 to fetus
Improved extraction of CO2 from fetus
Overall increased O2 carrying capacity of hemoglobin
Bohr effect explains the above findings
Shift in maternal O2 dissociation curve to the left
Response to maternal respiratory alkalosis
Hypercoagulable state
2x risk thrombosis during pregnancy
5.5x risk postpartum

28. Hematologic System: Symptoms and Physical Findings
Some edema is normal
Worsens as pregnancy progresses
Worse during the summer

29. Hematologic System: Diagnostic Tests
Already discussed physiologic anemia
WBC counts as high as 30k in labor not abnormal
Increased fibrinogen
Non-pregnant: mg/dL
Pregnant: mg/dL
No change in in vitro clotting times

30. Renal System

31. Renal System
Maintains fluid, solute and acid-base balance in response to changes of the cardiac and respiratory systems

32. Renal System: Anatomic Changes
Enlargement and dilation of kidneys and urinary collecting system
Primary anatomic change
Kidneys lengthen 1 cm
Distended renal vasculature
Dilated renal pelvis, calyces and ureters
Mechanical compression: uterine compression R>L
Hormonal: Progesterone  smooth muscle relaxation
Decreased bladder tone (progesterone)
 increased residual volume
Decreased bladder capacity (uterine compression)

33. Renal System: Functional Changes
Increased renal plasma flow accounts for majority of change
50% increase in GFR
 increased solutes presented to kidneys  urinary excretion
Glucose, water soluble vitamins, amino acids
No increase in proteinuria in normal pregnancy
Slight decrease in sodium (increased secretion but increased reabsorption)
Clinical correlation: Trace glucose on urine dip normal in pregnancy
Increased RAAS activity
Renin 10x higher
Angiotensin 5x higher
Clinical correlation: Women with preeclampsia have increased sensitivity to RAAS

34. Renal System: Symptoms
Urinary frequency
Stress urinary incontinence
Common triage complaint: Leaking amniotic fluid or urine?
Urinary stasis  increased UTI/pyelo
Clinical correlation: We treat asymptomatic bacteruria in pregnancy

35. Renal System: Physical Findings
Protrusion of bladder base into vagina
Pressure from fetus
 edema

36. Renal System: Diagnostic Tests
Decreased BUN
8-10 mg/dL in pregnancy
Decreased Creatinine
mg/dL in pregnancy
Proteinuria >300 mg/24 hours abnormal
Unchanged from non-pregnant state
Renal imaging
Hydronephrosis (R>L) often normal in pregnancy

37. GI System

38. GI System: Anatomic Changes
Enlarging uterus displaces stomach and intestines
No change in size
Liver and biliary tract unchanged in size
Portal vein enlarges d/t increased blood flow

39. GI System: Functional Changes
Blame the hormones!
Progesterone  smooth muscle relaxation
Decreased lower esophageal sphincter tone
Decreased GI motility
Decreased gallbladder contractility
Estrogen
Reduced intraductal transportation of bile acids
 cholestasis and cholelithiasis
Increased hepatic protein synthesis
 increased fibrinogen, numerous clotting factors and binding proteins

40. GI System: Symptoms Nausea/vomiting Hyperemesis
Progesterone, hCG and stomach relaxation
Hyperemesis
Can  weight loss, ketone formation, electrolyte imbalance
Dietary cravings/aversions
Pica
Ptyalism
GERD
Increased intraabdominal pressure, relaxation of LES (progesterone)
Constipation
Mechanical obstruction of bowel from uterus, reduced motility (progesterone) and increased H2O absorption

41. GI System: Physical Findings
Gingival disease
Gums more edematous and bleed easily
Hemorrhoids
Constipation and elevated venous pressure

42. GI System: Diagnostic Tests
Alkaline phosphatase: Doubled
Produced by placenta
Serum cholesterol: Increased
Serum albumin: Decreased
AST/ALT/GGT/bilirubin: Unchanged or slightly lower
Amylase/lipase: Unchanged

43. Endocrine System

44. Endocrine System: Thyroid Function
Overall euthyroid state
Gland enlarges
hCG and TSH have homologous alpha subunits
hCG can activate TSH receptor and lead to T4 secretion
Negative feedback reduces TSH levels (effect peaks at end of first trimester)
Estrogen increases hepatic synthesis of thyroxine binding globulin (TBG)
increase in total (protein-bound) T4 and T3
This form is not biologically active
Overall free T4 and T3 levels unchanged in pregnancy

45. Endocrine System: Adrenal Function
Size of adrenals unchanged in pregnancy
Estrogen increase hepatic synthesis of cortisol-binding globulin
 elevated cortisol
Increased ACTH (corticotropin)
Increased aldosterone
Increased deoxycorticosterone (estrogen influenced)
Decreased DHEAS (increased hepatic uptake)

46. Metabolism

47. Metabolism Carbohydrates Lipids Protein
Insulin resistance (hPL aka hPS)
Hyperinsulinemia
Glucose crosses placenta via facilitated diffusion for fetus
Overall fasting hypoglycemia and postprandial hyperglycemia
Clinical correlation: Gestational diabetes
Lipids
Increased levels
Clinical correlation: Don’t check lipids or triglycerides during pregnancy!
Protein
Higher protein intake and utilization

48. Other Systems

49. Musculoskeletal Lumbar lordosis Worsening of hernias or diastasis
Helps shift center of gravity but  back pain
Worsening of hernias or diastasis
Increased intraabdominal pressure
Increased laxity of joints/ligaments
Relaxin and progesterone
Pubic symphysis separation
Increased risk of falls from this and altered center of gravity
Calcium stores mobilized for fetus
Reduced total calcium
Increased maternal PTH to increase Ca absorption and reduce renal losses
No overall loss in bone density

50. Skin Spider angioma and palmar erythema Striae gravidarum
Estrogen
Striae gravidarum
Hyperpigmentation
Estrogen and melanocyte-stimulating hormone
Linea nigra
Melasma
Skin nevi can increase in size (need excision if rapidly increasing)
Increased eccrine sweating and sebum  acne
More hair follicles in growth (anagen) phase
Postpartum with relative increase in telogen (resting), so subjective hair loss

51. Skin
Linea Nigra
Melasma

52. Reproductive Tract Vulvar varicosities Leukorrhea of pregnancy
Increased vaginal transudate
Cervical ectropion
Eversion of endocervix
Enlargement of uterus via hypertrophy
Size regresses after delivery but slightly larger than pre-pregnancy
Increased size of uterine cavity after a delivery

53. Breasts
Rapid increase in size during first 8 weeks, then slower rate of increase
25-50% enlargement
Nipples and areola larger
Increased blood flow
Estrogen  ductal growth
Progesterone  alveolar hypertrophy
 pain or tenderness
Colostrum can be expressed at end of pregnancy

54. Ophthalmic Blurred vision
Increased thickness of cornea
Fluid retention
Decreased intraocular pressure
Regress postpartum
Clinical correlation: don’t recommend altering Rx for glasses or contacts during pregnancy

55. The Highlights When in doubt, blame progesterone! Renal CV Heme Pulm
Increased blood volume, cardiac output
Supine hypotension from IVC compression of uterus
Systolic murmur normal. Diastolic isn’t
Heart appears enlarged on CXR
Pulm
Respiratory alkalosis GI
Reflux, slowed transit, cholelithiasis
Renal
Hydronephrosis; R>L
Increased UTIs/pyelo
Creatinine lower
Heme
Thrombogenic state
Elevated WBC count in labor
Physiologic anemia because RBCs don’t expand as much as blood volume
Endocrine
Euthyroid (normal free T4/T3)
Low TSH, high total T4/T3
Insulin resistance

56. References
Beckmann, C.R.B. et al. Obstetrics and Gynecology. Seventh Edition