Maternal Physiology in Pregnancy Jennifer McDonald DO

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

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

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

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

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

Ovarian Changes Ovulation ceases Corpus luteum continues to grow until 7-8 weeks Corpus luteum secretes: 1. Estrogen 2.Progesterone 3.Relaxin

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

Hb concentrations falls from 14 gm/dL from 14 gm/dLTo 12 gm/dL. 12 gm/dL.

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

White Blood Cells Normal 7.0 mm 3 Rises to mm 3 Can rise as high as mm 3 in labor

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

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

Pulse 1 st trimester resting pulse increases by 8 beats/min By term increased by beats

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

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

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

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

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

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

Diaphragm At term diaphragm can be elevated up to 4 cm

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

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

Respiration Shortness of breath common perception by pregnant women Slight increase in respiratory rate Increased O 2 consumption 15-20% Increased TV with normal RR increased MV As MV increases hyperventiliation of pregnancy occurs lowering maternal CO 2 Over-breathing due to progesterone

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

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

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

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

Nausea & Vomiting 70% of pregnancies Elevated estrogen, progesterone Dramatic elevations in hCG Routinely resolves after weeks Hyperemesis gravidarum

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

Appendix Appendix displaced upwards & laterally later in pregnancy

Weight Gain BMI= Weight (kg)/height (m 2 )

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

Maternal Changes

Fetal Tissue Changes

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

Dermatologic Changes Linea nigra Cholasmsa

Stretch Marks Mechanical stretching of and rupture of elastic fibers Glucocorticoid influence

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