SM190 Normal Pregnancy Flashcards
Uterine adaptations to pregnancy
Total volume ranges from 5-20 L (compared to 10 mL in non-pregnant state)
Weight 1100 g (70 g non-pregnant state)
Hypertrophy as a result of estrogen and progesterone exposure
Progressive increase in uteroplacental blood flow as gestation advances
Cervical adaptations to pregnancy
Softens and undergoes cyanosis early
Hypertrophy and hyperplasia of cervical glands leads to eversion of proliferating columnar endocervical glands
Production of mucus rich in immunoglobulins, which act as a protective barrier against normal vaginal flora
Ovarian adaptations to pregnancy
Corpus luteum present and functional until 7 weeks gestation
Vascular pedicle increases from 0.6 cm to 2.6 cm at term
Decidual reaction (blastocyst contacts endometrium)
Luteoma causes exaggerated luteinization of ovary, may result in maternal virilization without effect on fetus
Theca lutein cyst: exaggerated physiological follicle stimulation (hyperreactive luteinalis), bilateral cystic ovaries, associated with high hCG levels (multiple gestation, GTD), maternal virilization occurs in 25% of patients with theca lutein cysts
Vaginal adaptations to pregnancy
Chadwick sign: increased vaginal vascularity that accounts for bluish-purplish color during pregnancy
Increase in mucosal thickness, loosening of connective tissue, hypertrophy of smooth muscle cells
Cardiac adaptations to pregnancy
Elevation of diaphragm results in displacement of heart upward and to the left (enlargement of silhouette on CXR)
50% increase in circulating blood volume
15% increase in HR
20-50% increase in CO
Vascular adaptations to pregnancy
First trimester: BP similar to pre-pregnancy levels
Second trimester: BP peaks, systolic rises 5-10 and diastolic rises 10-15
Third trimester: BP back to baseline values
Impairment of venous return by mechanical uterine obstruction and overall increase in SVR
Respiratory adaptations to pregnancy
Diaphragm elevates, subcostal angle increases, thoracic circumference increases
No change in RR
40% increase in tidal volume
20% decrease in RV and FRC
Dysnpea of pregnancy: results from increased TV that lowers maternal PCO2, which is required for proper CO2 diffusion from mom to fetus. Compensated for by increased excretion of bicarb.
Gastrointestinal adaptations to pregnancy
Displacement of stomach and intestines
Gastric emptying time unchanged during pregnancy, but increases substantially during labor (especially after analgesics are given)
Liver has minimal changes except it sees more blood. Alk phos and albumin are usually abnormal but not pathologic
Gallbladder contractility reduced, size can increase
Renal adaptations to pregnancy
Slight increase in kidney size
GFR increases by up to 50% mid-pregancy, with even greater increases in RPF. Serum Cr decreases normally in pregnancy
Uterine displacement of ureters results in ureteral dilatation
Increased bladder pressure with compensation by elongation of the urethra, which increases intraurethral pressure and maintains continence
Volemic adaptations to pregnancy
Hypervolemia:
Meets metabolic demands of the enlarged uterus and its hypertrophied vascular stem
Provides nutrients to support the fetus and placenta
Protects mom against the effects of impaired venous return in supine and erect positions and against effects of blood loss associated with parturition
Erythrocytic adaptations to pregnancy
Erythroid hyperplasia occurs and you see a slight increase in reticulocyte count (not abnormally high)
Erythrocyte volume increases by about 450 mL by the end of pregnancy
Increase in erythrocytes not as great as increase in blood volume, which leads to a slight decrease in Hb and Hct in pregnancy (Hb < 11.0 g/dL considered anemic)
Iron adaptations to pregnancy
1000 mg Fe required for pregnancy, with about 1/3 transferred to fetus and placenta
Leukocytic adaptations to pregnancy
Slight leukocytosis is not abnormal
More granulocytes and CD8’s, less CD4’s and monocytes
Coagulation adaptations to pregnancy
Augmented, but remain in balance to maintain homeostasis
All clotting factors increase, except XI and XIII
Protein S decreases, as does activated protein C
tPA increases throughout pregnancy
Minimal decrease in platelet count in pregnancy (due to hypervolemia)
Endocrine adaptations to pregnancy
Increased: estrogen, progesterone, prolaction, PTH, aldosterone, cortisol, DHEA, androstenedione, testosterone, T3/T4, TBG
TSH and TRH remain stable, TBG ranges can still be used
Metabolic adaptations to pregnancy
BMR increases 10-20% by end of pregnancy
Weight gain: normal weight gain attributable to uterus, amniotic fluid, fetus, placenta, breast size, and increase in intravascular volume and extracellular fluid. Pregnancy-related increase in energy demands are maximally 300 kcal/day (don’t need to “eat for two”)
Carbohydrate metabolism: normal pregnancy characterized by mild fasting hypoglycemia, postprandial hyperglycemia, hyperinsulinemia, and exaggerated suppression of glucagon
Protein metabolism: nitrogen balance increases with gestational age because of more efficient use of dietary protein
Fat metabolism: lipids, lipoproteins, and apolipoproteins increase dramatically in pregnancy, this is required for proper steroidogenesis. Fat storage occurs primarily mid-pregnancy and tends to be deposited more centrally rather than peripherally
Placental adaptations to pregnancy
Intervillous space:
Maternal blood bathes syncytiotrophoblast
Chorionic villi and intervillous space essentially function together to act as fetal “lungs, GI tract, and kidneys”
Fetoplacental circulation:
Separated from maternal blood by layer of fetal endothelium and syncytiotrophoblast
Regulation of placental transfer:
Concentration of substance in maternal plasma and the extent that it’s bound to a plasma carrier protein
Rate of maternal blood flow through intervillous space
Area available for exchange across villous trophoblast epithelium
Mode of transport (e.g. simple diffusion vs active transport)
Amount of substance metabolized by placenta during transfer
Area for exchange across fetal intervillous capillaries
Rate of fetal blood flow through villous capillaries
Fetal circulation adaptations to pregnancy
High pulmonary vascular resistance because fetal blood does not need to enter pulmonary vasculature in order to be oxygenated
Normal fetal shunts: (ductus venosus, foramen ovale, ductus arteriosus)
Circulatory changes at birth:
Closure of foramen ovale
Collapse of ductus venosus and umbilical vessels Closure of ductus arteriosus: alveolar expansion leads to increased alveolar capillary O2, increased O2 induces marked decrease in pulmonary vascular resistance, results in decreased RA pressure and afterload along with increased pulmonary vascular blood flow, backflow of oxygenated blood into ductus arteriosus results in production of prostaglandins leads to vasoconstriction/closure of ductus)
Fetal respiration adaptations to pregnancy
Fetal breathing movements begin between 16-22 weeks gestation
Anatomical maturation:
Pseudoglandular stage (5-16 weeks) Canalicular stage (16-25 weeks) Terminal sac/alveolar stage (25 weeks through 8 years of life) Production of surfactant by type II pneumocytes
Fetal gastrointestinal adaptations to pregnancy
Swallowing begins at 10-12 weeks
Fetal renal adaptations to pregnancy
Fetal kidneys begin to secrete urine early in pregnancy and accounts for majority of amniotic fluid volume after 16 weeks gestation
Fetal hematologic adaptations to pregnancy
Embryonic hemoglobin:
Several different embryonic hemoglobins are made as gestation progresses during early pregnancy
Made in yolk sac
Fetal hemoglobin
Composed of two alpha and two gamma chains
Produced in fetal liver
Increased oxygen affinity for oxygen that adult hemoglobin: O2 dissociation curve
Fetal endocrine adaptations to pregnancy
Thyroid: thyroid hormone critical for normal development, especially that of the brain, fetus starts synthesizing thyroid hormone at 10-12 weeks gestation. Dependent upon maternal thyroid hormone prior to this time
Adrenal glands: fetal adrenals at term weigh as much as adult adrenals because of large fetal zone that involutes rapidly after birth. Huge capability for steroid hormone production, precursor is cholesterol (primarily de novo production), contributes precursors that are converted by placenta to produce high levels of maternal estrogens
Normal labor and delivery
Mechanisms resulting in parturition:
Ultimately remain unelucidated in humans
Myometrial contractility: smooth muscle contractions mediated through ATP-dependent binding of myosin to actin, frequency of contractions corresponds to frequency of action potentials, force of contractions mediated by numbers of fibers activated
Mechanics of labor: power
Strength of contraction and appropriate frequency of contractions
Optimally 3-5 contractions in 10 minute period
External versus internal monitoring
Main mechanics of labor that can be affected by medical management
Mechanics of labor: passenger
Fetal size in relation to maternal pelvis impacts success of labor
“Fetal attitude”
Lie: long axis of fetus in relation to maternal long axis (longitudinal, transverse, oblique)
Presentation: pole of the fetus that overlies pelvic inlet (cephalic, breech)
Position: relationship of fetal presenting part to maternal pelvis (occiput anterior, occiput posterior, mentum anterior, mentum posterior)
Station: position of leading bony edge of presenting fetal part to maternal ischial spines (3 or 5-point scale, position of leading bony edge of presenting fetal part to maternal ischial spines)
Mechanics of labor: passage
Maternal bony pelvis: Sacrum, ilium, ischium, pubis
Pelvic shapes: gynecoid, anthropoid, android, platypeloid
Pelvic muscles facilitate rotation and delivery
Stage 1 of labor
Interval between onset of labor and full cervical dilation
Latent: onset of painful contractions to point of change in slope of labor curve (usually 3-4 cm, but variable), duration varies and can range up to 14 hours for multiparous women and 20 hours for nulliparous women
Active: period of rapid cervical change, anticipate at least 1.2 cm change/hr for nulliparas and 1.5 cm change/hr for multiparas
Stage 2 of labor
Interval between full cervical dilation and delivery of fetus
Can last up to 3-4 hours in nulliparas with epidural analgesia (2-3 hours without) and 2-3 hours in multiparas with epidurals (1-2 hour without)
Stage 3 of labor
Interval between delivery of neonate to delivery of placenta
Usually occurs within 10 minutes of delivery, but up to 30 minutes is normal
