Maternal Physiology in Pregnancy

1. Maternal Physiology in Pregnancy Jennifer McDonald DO

2. Role of Estrogen in Pregnancy • Increases blood flow to uterus by promoting vasodilation • Changes the sensitivity of the system to CO2 • Softens cervix, initiates uterine activity, maintain labor • Develops breast tissue in preparation for breast feeding

3. Role of Progesterone in Pregnancy • Readies the uterus for implantation • Relaxes smooth muscle to prevent SAB • Prevents maternal immunologic response to fetus • Relaxes smooth muscle • Plays role in development of alveoli & ductal system in the breast

4. Changes in Size Increases from 50 g to 1000 grams ! Volume changes from 4 mL to over 4000 mL

5. Uterine blood flow increases progressively and reaches 500 mL/minute at term

6. Cervical & Vaginal Changes • Cervix becomes hypertrophied, soft and bluish in color • Thick secretions fill the endocervical canal (“mucous plug”) • “Chadwick’s” sign – bluish color to cervix/vagina due to increased vascularity

7. Ovarian Changes • Ovulation ceases • Corpus luteum continues to grow until 7-8 weeks • Corpus luteum secretes: • Estrogen • Progesterone • Relaxin

8. Blood Volume • Increases 35-45% by 32 weeks • Red blood cell mass increases by 33% The increase in plasma is greater and faster than RBC resulting in physiologic anemia

9. Hb concentrations falls from 14 gm/dL To 12 gm/dL.

10. Purpose of Increase • Meets increased demands of uterus & baby • Protects against supine hypotension syndrome • Protects against fluid loss in labor

11. White Blood Cells • Normal 7.0 mm3 • Rises to 10.5-11 mm3 • Can rise as high as 15-16 mm3 in labor

12. Coagulation Factors • Fibrinogen doubled • Factor VIII tripled • Factor VII and Factor X are doubled Pregnancy is a hyper-coaguable state

13. Cardiovascular Changes • Apex displaced upwards and to the left • Heart size increased 12%

14. Pulse • 1st trimester resting pulse increases by 8 beats/min • By term increased by 15-20 beats

15. Heart Sounds • First heart sound becomes louder and may split • Intensity of the second sound may become louder • Systolic functional murmurs develop in most due to tricuspid regurgitation

16. Cardiac Output • Increases 40% by 20 weeks • Mainly due to increases in SV • Maintained until 4 days post-partum CO = HR x Stroke volume

17. Blood Pressure • Systemic blood pressure overall decreased • Systolic changes little • Diastolic reduced (5-10 mmHg) • Venous pressure upper body unchanged • Venous pressure in the lower body increased • Especially affected by position

18. Supine Hypotension • Compression of the inferior vena cava • Decreased venous return • Decreased cardiac output • Lowered blood pressure

19. Peripheral Vasodilatation • Increased blood flow to the skin especially hands & feet lead to a feeling of warmth • Increased congestion of nasal mucosa leading to nasal congestion • Epistaxis common

20. Venous Pressure • Mechanical pressure on the pelvic veins • Increased venous return from the internal iliac veins  increased pressure in the external iliac veins • Increased pressure in lower extremities predisposes women to edema & varicose veins

21. Diaphragm At term diaphragm can be elevated up to 4 cm

22. Diaphragm • Mobility reduced • Respiration becomes mainly thoracic • Widened subcostal angle increasing transverse diameter of the chest

23. Respiratory Physiology TV  (30-50%) TLC  (4-5%) FRC  (20%) RV  (20%) ERV  (20%) IC  (5-10%)

24. Respiration • Shortness of breath common perception by pregnant women • Slight increase in respiratory rate • Increased O2 consumption 15-20% • Increased TV with normal RR increased MV • As MV increases hyperventiliation of pregnancy occurs lowering maternal CO2 • Over-breathing due to progesterone

25. Renal Changes • Renal blood flow and GFR increased by as much as 50% • Increased excretion • Decreased serum creatinine & uric acid

26. Ureters Dilatation of the ureters and renal pelvis Due to … • Relaxation by progesterone • Pressure at the pelvic brim especially on the right

27. Urinary Frequency • Pressure on the bladder by the enlarging uterus • Congestion of the bladder mucosa

28. GI Changes • Gingivitis • Reduced sensitivity of taste buds • Pica • Decreased GI motility due to progesterone • Increased propensity toward gallbladder disease

29. Nausea & Vomiting • 70% of pregnancies • Elevated estrogen, progesterone • Dramatic elevations in hCG • Routinely resolves after 12-14 weeks • Hyperemesis gravidarum

30. Constipation • Decreased motility • Increased water absorption • Pressure on the sigmoid colon • More sedentary • Iron from prenatal vitamins

31. Appendix Appendix displaced upwards & laterally later in pregnancy

32. Weight Gain BMI= Weight (kg)/height (m2)

33. Distribution • 6 kg maternal tissues (breast enlargement, blood volume, fat stores) • 5 kg fetal tissues (baby, placenta, amniotic fluid) 7 kg Water 3 kg fat 1 kg protein

34. Maternal Changes

35. Fetal Tissue Changes

36. Musculoskeletal Changes • Increased mobility of pelvic joints Progesterone & Relaxin • Flattening of feet • Progressive lordosis • Round ligament pain

37. Dermatologic Changes Linea nigra Cholasmsa

38. Stretch Marks • Mechanical stretching of and rupture of elastic fibers • Glucocorticoid influence

39. Breast Changes • Due to increased estrogenic state • Increased size & vascularity • Mastodynia very common • Increased pigmentation of areola & nipple • Prominence of Montgomery tubercles