Physiologic Changes of Normal Pregnancy Flashcards
Vaginal microbiome
Increased estrogen → increased glycogen → increased lactic acid production → diversity decreased, lactobacillus prominent
Gut microbiome
Increased bacterial load in intestines, decreased diversity. Stool indicates proinflammatory
Placental microbiome
Not necessarily sterile as previously thought. Resembles oral bacteria. Interesting implication for link between periodontal disease and preterm birth.
Uterine changes
- Size: 70 grams with 10 ml capacity increases to 1100 grams with up to 20 L capacity
- Muscle cells: hyperplasia (esp. early) and hypertrophy
- Contractility – Longitudinal and circular muscles of the uterus gain contractile equilibrium by term.
- Contractions start in 2nd trimester, usually person isn’t aware of them
- Influenced by electrical events in myocyte cell membrane, propagation over gap junctions and also intracellular calcium availability.
- Suppressed by progesterone, prostacyclin, relaxin, NO, CRH
- Blood volume - increases
Cervical changes
- Normally comprised of mostly connective tissue (collagen, elastin, proteoglycans, cells) and little smooth muscle (color, gland).
- Hormones → change collagen/glycosaminoglycans structure → cervix softens
- May have more noticable ectropion
- Produces copious amounts of thick, acidic mucus → composition changes over course of pregnancy as role shifts from cervical remodeling to stopping ascending infections
Ovarian changes
- Function: quiet 2nd and 3rd Trimesters
- Corpus luteum – Primary source of progesterone, stops after 7 weeks
Vagina changes
- Increased vascularity and hyperemia (Chadwick’s sign). Varicose veins of vulva may get worse
- Connective tissue underlying vaginal epithelium relaxes
- Muscles fibers thicken
- pH of vaginal secretions DECREASES
- Increased estradiol → increased glycogen → metabolized into lactic acid by lactobacilli
Breast changes
- Size increases (hypertrophy of glandular epithelium and secretory alveoli)
- Color of areola darkens
- Montgomery gland enlargement
- Secretions
- Vascularity increases
- Development of lactation (pituitary secretion of prolactin).
Chadwick’s sign
Blue-ish color that eventually spreads to all of the vaginal mucosa (as early as 6 weeks gestation).
- Due to increased vascularity/hyperemia
Goodell’s sign
Softening of the cervix
Hegar’s sign
Softening of the LUS so much it can be compressed during a bimanual
(LUS = lower uterine segment)
GI changes
Progesterone
- Decreases esophageal sphincter tone
- Reflux/heartburn
- Slows peristalsis and intestinal transit time
- Better water/nutrient absorption
- Dryer/harder stools/constipation.
- Increased bile volume, bile stasis, cholesterol formation
- Increased risk for gallstones
Increased appetite → food cravings or pica
Estrogen
- May have swelling or epulis
- Risk for periodontal disease. Doesn’t worsen tooth decay or loss
Pytalism – excessive salivation often because of swallowing secondary to N/V
Liver and biliary adaptations
- Doesn’t change in size or blood flow
- Plasma proteins decrease due to hemodilution
- Progesterone stimulates CYP450
Genitourinary changes
Anatomical changes
- Grow in volume and length
- Ureters dilate due to compression from big uterus and slow urine flow (R > L) → hydroureter
- May also be due to hormones like progesterone
Renal plasma flow up by 60-80% by midpregnancy (decreases closer to term. Increased blood and extracellular fluid volumes and maternal/fetal waste
- GFR increases within 2 weeks of conception, by 50% at 12 weeks
- Increased creatinine clearance, decreased serum creatinine, BUN, serum osmolarity
- Renal tubular function → Na++ retention due to estrogen, deoxycorticosterone and RAAS. K+ also retained
- Lay left lateral for best renal blood flow
Increased risk of urine stasis and infection
Decreased bladder capacity and more incontinence due to pressure in 3rd trimester. Pressure from fetal presenting part can slow blood/lymph drainage and increase risk of infection too
Increased glucose excretion
- 15% of normal pregnancies will have glycosuria (risk for UTI)
Respiratory changes
- Anatomic changes
- Estrogen + increased blood volume → capillary engorgement → increased mucous production in nose/sinuses/ears
- Progesterone = vasodilatory → mucous membrane swelling
- Increased incidence of rhinitis, epistaxis, serious otitis, and sinus congestion
- Relaxin → chest cartilage pliability
- Diaphragm rises with growth of gravid uterus (4 cm), thoracic circumference increases 6 cm
- Most changes in chest wall persist post pregnancy
- Physiology
- Progesterone affects RR, respiratory drive, and total pulmonary resistance.
- Decreases pulmonary airway resistance
- Stimulates respiratory center in brainstem to increase RR and lower CO2 threshold
- Increased metabolism → Increased O2 requirements/consumption
- Mild hyperventilation and respiratory alkalosis
- Respiratory parameters that decrease: total lung capacity, expiratory reserve capacity, residual volume, total pulmonary resistance
- Respiratory parameters that increase: Inspiratory capacity, tidal volume, minute ventilation, O2 consumption
Cardiovascular changes
- Increased ventricular muscle mass in 1st trimester
- C.O increases by 30 – 50 %, about half by 8 weeks, both due to SV and HR
- Needed for 10x increase in uterine blood flow and 50% extra to kidneys. Also more to breast and skin
- HR increases at 5 weeks, reaches max of 15-20 bpm > than usual by 32 weeks
- Vascular adaptations
- Collagen softens throughout vascular system → increased compliance and decreased vascular resistance around 5 weeks.
- → slower venous flow → risk for clots
- Progesterone and prostaglandin have relaxant effect
- Low resistance uteroplacental circulation → lower vascular resistance
- Collagen softens throughout vascular system → increased compliance and decreased vascular resistance around 5 weeks.
- Increased sensitivity to autonomic blockade → sudden drop of BP with epidural anesthesia
- Several signs and symptoms mimic cardiac disease – diagnostic dilemma
- 4% pregnant women have unrecognized CVD
- Dyspnea – progesterone effect on breathing centers
- Fatigability – response to increased metabolic demand
- Dependent edema – venous pressure from uterus, lower colloid osmotic pressure
- 1st heart sound louder – early closure of mitral valve
- Split S2 – expected at 30 weeks
- S3 – heard in 90% of pregnant women
- Systolic flow murmur – 95% pregnant women – begins between 12-20 weeks and disappears within a week post-birth
- Left lateral displacement of PMI - gravid uterus pressing on diaphragm/heart
- Mammary soufflé – continuous murmur from mammary vessels best heard in the 2nd inter costal space
