SM190 Normal Pregnancy

Question 1

Uterine adaptations to pregnancy

Answer 1

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

Question 2

Cervical adaptations to pregnancy

Answer 2

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

Question 3

Ovarian adaptations to pregnancy

Answer 3

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

Question 4

Vaginal adaptations to pregnancy

Answer 4

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

Question 5

Cardiac adaptations to pregnancy

Answer 5

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

Question 6

Vascular adaptations to pregnancy

Answer 6

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

Question 7

Respiratory adaptations to pregnancy

Answer 7

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.

Question 8

Gastrointestinal adaptations to pregnancy

Answer 8

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

Question 9

Renal adaptations to pregnancy

Answer 9

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

Question 10

Volemic adaptations to pregnancy

Answer 10

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

Question 11

Erythrocytic adaptations to pregnancy

Answer 11

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)

Question 12

Iron adaptations to pregnancy

Answer 12

1000 mg Fe required for pregnancy, with about 1/3 transferred to fetus and placenta

Question 13

Leukocytic adaptations to pregnancy

Answer 13

Slight leukocytosis is not abnormal

More granulocytes and CD8’s, less CD4’s and monocytes

Question 14

Coagulation adaptations to pregnancy

Answer 14

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)

Question 15

Endocrine adaptations to pregnancy

Answer 15

Increased: estrogen, progesterone, prolaction, PTH, aldosterone, cortisol, DHEA, androstenedione, testosterone, T3/T4, TBG

TSH and TRH remain stable, TBG ranges can still be used

Question 16

Metabolic adaptations to pregnancy

Answer 16

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

Question 17

Placental adaptations to pregnancy

Answer 17

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

Question 18

Fetal circulation adaptations to pregnancy

Answer 18

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)

Question 19

Fetal respiration adaptations to pregnancy

Answer 19

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

Question 20

Fetal gastrointestinal adaptations to pregnancy

Answer 20

Swallowing begins at 10-12 weeks

Question 21

Fetal renal adaptations to pregnancy

Answer 21

Fetal kidneys begin to secrete urine early in pregnancy and accounts for majority of amniotic fluid volume after 16 weeks gestation

Question 22

Fetal hematologic adaptations to pregnancy

Answer 22

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

Question 23

Fetal endocrine adaptations to pregnancy

Answer 23

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

Question 24

Normal labor and delivery

Answer 24

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

Question 25

Mechanics of labor: power

Answer 25

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

Question 26

Mechanics of labor: passenger

Answer 26

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)

Question 27

Mechanics of labor: passage

Answer 27

Maternal bony pelvis: Sacrum, ilium, ischium, pubis

Pelvic shapes: gynecoid, anthropoid, android, platypeloid

Pelvic muscles facilitate rotation and delivery

Question 28

Stage 1 of labor

Answer 28

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

Question 29

Stage 2 of labor

Answer 29

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)

Question 30

Stage 3 of labor

Answer 30

Interval between delivery of neonate to delivery of placenta

Usually occurs within 10 minutes of delivery, but up to 30 minutes is normal