Physiological changes in pregnancy

Cardiovascular

40-50% ­ plasma blood volume

Vasodilation, with resultant ­ heart rate (15-20 bpm), ­ stroke volume (20-30%), cardiac output (CO) (30-50%)

Uterine perfusion goes from 2% of CO to 17%

¯ Systemic vascular resistance secondary to smooth muscle relaxation caused by ­ progesterone

¯ BP (up to 21%) between 8-26 weeks

Preexisting HTN may be artificially masked

Compression of venous and lymphatic drainage of legs

Leads to lower extremity edema, stasis, increased DVT risk, and resultant 10-30% ¯ in CO

Vena cava may be completely occluded in the supine position late in pregnancy

Heart is displaced left and upward

Heart appears larger on chest film

Diagnosis of cardio-megaly should not be based on CXR alone

Jugular venous distention after 20 weeks

 

These and other signs/ symptoms may mimic cardiac disease

Development of systolic ejection murmur

Developed by up to 96% of gravidas

estrogen leads to edema ­ mucous production of nasopharynx

Gravidas commonly have congestion/stuffiness and may have epistaxis

Gravidas may complain of chronic cold-like symptoms

Pulmonary

Tidal Volume (30-40%)

 

All of these changes may lead to a relative dyspnea. 75% of women complain of dyspnea by term.

¯ Total lung capacity (5%) from elevation of a diaphragm

Diaphragm may rise 4cm on chest film

¯ Functional residual capacity (20%)

 

Tidal volume and Minute ventilation (30-40%)

Leads to ¯ PaCO2 and a compensated respiratory alkalosis

Metabolic

protein and carbohydrate metabolism

One kilogram of extra protein is deposited to the placenta, uterus, fetus, breast tissue, hemoglobin, and plasma proteins

 

 

 

Nutrition

Caloric requirements by 200 kcal/day

Gain of 25-35 lbs throughout pregnancy

 

protein requirement to 70-75 g/day

 

 

Folate requirement (0.4 to 0.8 mg/day)

May lead to neural tube defects if not supplemented

PNV

Hematologic

40-50% ­ in plasma blood volume, but only 20-30% ­ in red cell volume

Leads to relative, dilutional anemia. These changes peak at 30-34 weeks

Screen for underlying anemia which may exacerbate physiologic anemia and provide iron

WBC may increase as high as 20 mil/mL

 

 

Platelet count may decrease to as low as 100-150 mil/mL

 

 

¯ Factors XI, XIII

Alteration in these factors leads to hypercoagulability. Pregnancy also is a state of venous stasis and endothelial damage.

 

 

procoagulant factors (Factors I (Fibrinogen), VII, VIII, IX, X)

 

Renal

Size of kidneys and ureters

Right ureter dilated > left ureter, both by mechanical effect of uterus and relaxation by progesterone

Increased incidence of pyelonephritis

Mechanical compression and displacement of ureters

GFR by 50% (which may last until 20 weeks postpartum)

Values ­ to 150-200 ml/min

 

¯ BUN (from 13 to 9) and Creatinine (from 0.8 to 0.5)

 

 

Glucosuria (due to saturated tubular reabsorption)

 

 

Plasma rennin activity (5-10x) and angiotensin (4-5x)

Leads to ­ aldosterone (2x) and ­ sodium reabsorption

 

Nocturia

 

 

Gastrointestinal

b-hCG, relaxation of smooth muscle

Leads to nausea and vomiting usually resolved by 14-16 weeks

70% of pregnancies affected by “morning sickness”

gastric emptying time

 

 

¯ gastroesophageal sphincter tone

Leads to acid reflux

 

¯ colonic motility

Leads to ­ water absorption and constipation

11-38% of gravidas complain of constipation

Portal venous pressure

Dilation of portosystemic venous anastomoses

Hemorrhoids

Uterine displacement of bowel

Appendix may be greatly displaced

Diagnosis of appendicitis made difficult

¯ rate of gallbladder emptying, change of bile fliud

Leads to increased formation of gallstones

Retained bile salts may lead to pruritus

Endocrine

b-hCG

 

 

estrogen

Leads to ­ in thyroxine-binding globulin

Keep mother euthyroid in spite ¯ serum iodid levels

human placental lactogen (hPL)

Causes lipolysis and antagonizes insulin

 

progesterone

Relaxes smooth muscle

 

Prolactin (10x at term)

Prepares breasts for lactation

 

Alkaline phosphatase (2-4x)

Produced by placenta

 

Dermatologic

estrogen

Can lead to formation of spider angiomata and palmar erythema

Angiomata are seen in up to 70% of caucasians

melanocyte stimulating hormone (MSH)

 

 

 

Hyperpigmentation of nipples, umbilicus, linea nigra, perineum, and face (melasma/chloasma). Nevi may increase in size and frequency.

Some hyper-pigmentation occurs in 90% of gestations. Chloasma occurs 70% of the time

Stretch and steroids/estrogen lead to striae distensae (stretch marks)

These are permanent changes that will change from pink/purlple to white/silver with time

No effective prevention exists

cortisol and placental androgens may lead to ­ hirsutism

Face mostly affected

 

hair loss 2-4 months after delivery

Telogen effluvium, usually restored by 6-142 months postpartum.

 

acne

Related to ­ oil production by sebaceous glands

 

Musculoskeletal

Gravid uterus leads to progressive lordosis of the spine in order to prevent change in the maternal center of gravity

 

Leads to lower back pain

Relaxin leads to relaxation of the ligaments of pubic symphysis and sacroiliac joints, peaking between 28-32 weeks

Symphis width increases from 3-4 mm to nearly 8 mm

Leads to pain over pubis and in inner thighs

Other

Breasts enlarge during first 8 weeks due to vasocongestion, and afterwards from ductal and alveolar growth

Nipples and areaola enlarge and nipples become more mobile

Breast pain is common complaint early in pregnancy

3% ­ in corneal thickness due to edema, and ¯ intraocular pressure (10%)

Eyeglasses, contact lenses, or laser-eye surgery may be affected during pregnancy but will resolve within a few weeks postpartum

 

 

vascularity and hyperemia of genital tract

Bluish discoloration of cervix (Chadwick’s sign); softening and cyanosis of cervix (Goodell’s sign)

 

 

vascularity and hyperemia of the gums

Can lead to gingivial bleeding, superinfection