LM 15.1: Normal Physiologic Changes of Pregnancy Flashcards
what are maternal adaptations to pregnancy ?
almost every organ system changes in response to pregnancy, some more significantly than others
most changes resolve by 6 weeks post delivery once all of the hormonal influences have cleared
how does the uterus change from non-pregnant to pregnant state?
not pregnant uterus: 70 grams, 10 mL cavity capacity
pregnancy uterus: 1100 grams after delivery, 5 L cavity capacity but up to 10 L if multiple gestation or abnormal amniotic fluid
what causes growth of the uterus during pregnancy?
enlargement is not by production of new cells, but by hypertrophy of the myometrial cells already present
early in pregnancy, hypertrophy likely is influenced by estrogen
at approximately 12 weeks, the uterus is large enough to extend out of the pelvis
late in the 3rd trimester it is causing elevation of the diaphragm
how does blood blow into the uterus change during pregnancy ?
blood flow into the uterus increases progressively throughout the pregnancy
2nd trimester: 450 ml/min of blood flow
at term: 500-750 ml/min
what are the 3 layers of the uterine wall?
- outer hoodlike layer
covers fungus and extends into ligaments
- middle layer
interlaced with blood vessels, myocytes running in different directions
- inner layer
sphincter like fibers around the tubal ostia and internal os of cervix
how does myocyte structure in the uterus help with pregnancy ?
in the myometrium, there are myocytes running in different directions
they have a double curve to increase the interlacing of cells and strength
this allows for creating the strength of the contractions as well as the direction of the force towards the cervix
once placenta delivered, the uterus contracts down—these myocytes have now contracted around the vessels and stopped bleeding by mechanical means of closing the vessels
what is the blood supply of the placenta?
spinal arteries
which medications cause uterine contraction?
- oxytocin
- methylergonovine
- carboprost (F2alpha prostaglandin)
- misoprostol (E1 prostaglandin analog)
how does the cervix change throughout pregnancy?
early in pregnancy, the cervix takes on a bluish tinge from the increase in vascularity and changes in the collagen network (aka Chadwick Sign)
during the majority of the pregnancy, the cervix has the responsibility of retaining the pregnancy (holding it in)
the mucous produced by the cervix during pregnancy is thick, tenacious and rich in immunoglobulins and cytokines so it may act as a barrier to infection
by delivery time, the cervical glands have proliferated to the point of contributing half of the cervical volume
for delivery, the cervical matrix changes, allowing cervical change/dilation in response to contractions. The mucous thins and the mucous plug (thick mucous that was in the canal) is released
at delivery, the cervix has dilated up to 10 cm to allow passage of the fetus (it may have dilated from 1 to 10 cm in under 24 hours or less!)
what is the normal pH of the vagina? what maintains it?
between 3.5 and 6
it’s maintained by the production of lactic acid by Lactobacillus
how does the vagina change during pregnancy?
- epithelial thickening
- connective tissue loosening
- smooth muscle cell hypertrophy
how does skin change during pregnancy?
found in up to 90% of women
most noticeable in women of darker skin tones
not fully understood, but thought to be due to higher levels of Melanocyte stimulating hormone – estrogen and progesterone may play a role
examples:
1. linea nigra
- cloasma
- striae gravidarum
- angiomas
- palmar erythema
what is the linea nigra?
darkly pigmented vertical line found in the midline of the abdominal wall of pregnant women
what is cloasma?
AKA melasma gravidarum or the mask of pregnancy
also can be found in association with combination oral contraceptive agents
how does hair change during pregnancy?
- anlagen phase is lengthened in pregnancy (growth phase)
2. telogen effluvium = excessive hair loss in the postpartum period
how is water metabolism effected with pregnancy?
increased water retention caused by a reset of osmotic thresholds for thirst and vasopressin secretion
starts in early pregnancy and results in a decrease of plasma osmolality of 10 mOsm/kg –> by the end of the pregnancy, pregnant woman has retained approximately 6.5 L (14.3 lbs)
there may also be peripheral edema due to combination of decrease in osmolality and increase in venous pressure due to pelvic mass (pregnant uterus)
how do glucose levels change in pregnancy?
- mild fasting hypoglycemia
- postprandial hyperglycemia
- hyperinsulinemia
- hepatic gluconeogensis is augmented especially in 3rd trimester
what is gestational diabetes?
glucose intolerance that occurs during pregnancy and usually resolves by 6 weeks post delivery
because of the increased insulin resistance, diagnosis of diabetes increases
untreated gestational diabetes causes increased maternal AND fetal morbidity and mortality
what are the risk factors for gestational DM?
- history of gestational diabetes
- multiple gestation
- history of large for gestational age infant
- high risk race or ethnicity
- history of CVD
- physical markers of insulin resistance like obesity, acnthosis nigricans
- overweight
- family history of DM
- chronic HTN
- history of PCOS
what are the cardiovascular changes that occur during pregnancy?
- systemic vascular resistance drops at 5 weeks
- BP lowers around 16-20 weeks then rises after that
- CO increases due to increased HR
- blood volume increase
- as diaphragm is pushed up, heart is shifted to the left and up, rotated on the long axis leading to larger cardiac silhouette on CXR and slight left axis deviation on EKG
- exaggerated splitting of first heart sound, early systolic murmur without radiation
- EF doesn’t change
- supine hypotension due to the vena cava being compressed by uterus and decreasing venous return
what is supine hypotensive syndrome?
arterial compression by the pregnant uterus occurring in the supine position usually in the 3rd trimester or 2nd trimester if multiple gestation
the vena cava is compressed markedly decreasing venous return resulting in supine hypotension and poor maternal and placental(fetal) perfusion
increase in the venous system due to the mass effect of the pregnant uterus leads to increased venous pressure in the pelvis and lower extremities which leads to increased:
1. venous varicosities of pelvis, vulva, vagina and legs
- risk of DVT
- incidence of hemorrhoids
- lower extremity edema
how is blood volume effected during pregnancy?
blood volume increases by 15% in the firs trimester and by 40-45% by 32-34 weeks gestation –> this is accomplished by increases in plasma volume and in erythrocyte numbers
increase in red cell production is due to increase in erythropoietin and is reflected with increase in reticulocyte count
Hb and Hct decline due to greater production of plasma than RBCs resulting gin a dilution decrease in Hb/Hct and decreased viscosity –> this protects the mother from negative effects of standing or lying on back resulting in impaired venous return and from anticipated blood loss with delivery
how is coagulation/fibrinolysis effected during pregnancy?
pregnancy is a hyper coagulable state
coagulation and fibrinolysis are both augmented
level and rate of thrombin production increases progressively
- increase in fibrinogen
- increase in procoagulants
- liver stimulated by estrogen
what are the natural inhibitors of coagulation? how are they effected during pregnancy?
- protein C
- protein S
- antithrombin
resistance to activated protein C increases during pregnancy
decrease in free protein S levels
what are the structural changes that happen to the respiratory system during pregnancy?
- subcostal angle increases from avg of 68.5 degrees to 103.5 degrees
- diaphragm is elevated 4 cm from normal position in late 3rd trimester
- thoracic circumference increases ~6 cm
what are the physiologic lung changes that occur during pregnancy?
- functional residual capacity decreases by 20-30%
- residual volume decreases more than the expiratory reserve volume (ERV+RV = FRC)
- inspiratory capacity increases by 5-10%
- tidal volume and resting minute ventilation increase as pregnancy advances
- peak expiratory flow rate increases with gestation
- airway conductance increased
- total pulmonary resistance decreased
lung compliance, maximum breathing capacity, and forced vital capacity are unaffected
why does resting minute ventilation change during pregnancy?
resting minute ventilation increases due to:
- stimulatory action of progesterone
- low expiratory reserve volume
- compensated respiratory alkalosis
why do pregnant women note an increased desire to breath?
greater tidal volume during pregnancy lowers the PCO2 since you’re blowing off more CO2 and causing a respiratory alkalosis (PCO2 of 25-33 in 3rd trimester)
likely caused by progesterone which acts centrally to lower the threshold and raises sensitivity of chemorelfex response to CO2
this results in a lower HCO3 as well since it’s compensating for the respiratory alkalosis
it’s totally normal and can be misunderstood as a sign of CVD or respiratory disease
how do pregnancy women compensate for the respiratory alkalosis that occurs during pregnancy?
O2 affinity in RBCs is increased (Bohr effect)
slight increase in pH stimulates increase in 2,3-BPG in RBCs
PO2 is unchanged
how is the GFR effected in pregnant women?
increased GFR
25% by the 2nd week of conception!!!! 50% by the beginning of the 2nd trimester
occurs due to hypervolemia-induced hemodilution lowering the protein concentration and oncotic pressure of plasma entering the glomerular microcirculation
renal plasma flow increases by 80% by the end of the first trimester and then declines after 20 weeks
leads to:
1. increased frequency of urination due to increased in volume
- decrease in serum creatinine (0.4-0.9)
how are the kidneys effected in pregnancy?
- glucosuria
can be normal due to increased GFR and impaired tubular reabsorption
- proteinuria
due to increase in GFR and possible reduction of tubular reabsorption
300 mg/24 hrs compared to 150/24 hrs for non-pregnant female
how are the ureters effected by pregnancy?
- uterus enlarges, resists out of the pelvis and can compress the ureters at the pelvic brim
- progesterone causes relaxation of the ureters = dilation and stasis
- ureteral dilation; can lead to hydronephrosis
how is the bladder effected during pregnancy?
as pregnancy progresses, the space for the bladder to expand with collected urine decreases
vesicoureteral reflex can occur
signs/symptoms:
1. urinary frequency
- urinary incontinence
- increased risk for UTI and pyelonephritis
- higher risk of urosepsis
what are the intestinal changes that occur during pregnancy?
- intestines displaced upward – alters location of appendix and increases pressure on stomach
- progesterone slows GI motility, relaxes esophageal sphincter and leads to delayed gastric emptying with labor and narcotics
leads to constipation, heart burn, increased risk of aspiration at time of cesarean or other surgeries
what is hyperemsis gravidarum?
excessive nausea and vomiting during pregnancy
can lead to:
- dehydration
- ketosis
- weight loss
- electrolyte imbalance
- alkalosis due to HCl loss
- hepatic dysfunction
how is the liver effected during pregnancy?
- alkaline phosphatase almost doubles due to production of same by the placenta
- serum albumin declines
liver enzymes, GGT and bilirubin should not rise and may be slightly lower
how is the gallbladder effected during pregnancy?
- contractility reduced
leads to increased residual volume; may be due to progesterone
- increase of cholesterol saturation of bile
- cholelithiasis
how is the pituitary gland effected during pregnancy?
increases in size 135% largely driven by estrogen stimulated hypertrophy and hyperplasia of lactotrophs
normalized size by 6 months postpartum
how do prolactin levels change during pregnancy?
at term, prolactin levels are 10 time what they are in non-pregnant women
they return to normal after delivery even in breastfeeding women
how is the thyroid effected during pregnancy?
- TRH has no change
- thyroid gland production increases 40-100% to meet maternal and fetal demands so moderate enlargement occurs
- TSH levels decline
- TBG increases
how are TSH levels effected during pregnancy?
TSH and hCG share the same α-subunit.
hCG has intrinsic thyrotropic activity and can cause thyroid stimulation
TSH levels decline in >80% of women in the first trimester, but remain in the normal range
how are TBG levels effected during pregnancy?
thyroid binding globulin increases as a result of estrogen stimulation for higher liver production and lower metabolism rate due to sialylation and glycosylation of TBG
higher TBG increases Total T4 and Total T3 but does not change Free T4 or Free T3
maternal T4 crises the placenta and maintains normal fetal thyroid function so the fetus relies on lateral T4!
