↑ Intraabdominal pressure through uterine growth → dyspnea (the diaphragm is displaced upwards → ↓ total lung capacity, residual volume, functional residual capacity, and expiratory reserve volume)
Progesterone stimulates the respiratory centers in the brain → hyperventilation (to eliminate fetal CO2 more efficiently) → physiological, chronic compensated respiratory alkalosis
Elevated progesterone levels trigger a sensation of shortness of breath and stimulate the hypothalamus to increase respiratory drive.
Facilitated by increased diaphragmatic excursion and hormone-induced laxity of the intercostal muscles that allows for enlargement of the thoracic cavity (although the expanding uterus displaces the resting position of the diaphragm upward, diaphragmatic excursion is not impaired).
↓ PCO2 (∼ 30 mm Hg)
Slight increase in respiratory rate
Renal system
↑ Renal plasma flow → ↑ GFR → ↓ BUN and creatinine
Increased cardiac output leads to increased renal perfusion.
Therefore, serum creatinine levels considered normal in nonpregnant patients (eg, 1.0 mg/dL) represent significant renal dysfunction in this population.
↑ Glucose levels in urine: Increased glomerular filtration results in overload of the glucose carrier responsible for its resorption.
Mild proteinuria: Increased GFR and glomerular permeability to albumin increases protein excretion.
Hematologic system
↑ Plasma volume → ↓ hematocrit, especially towards the end of pregnancy (30–34th week of gestation) → dilutional anemia (hemoglobin value rarely drops below 11 g/dL)
Hypercoagulability is due to an increase in fibrinogen, factor VII, and factor VIII and a decrease in protein S (reduces the risk of intrapartum blood loss).
↑ RBC mass (increases from 8–10th week of gestation until the end of pregnancy)
↓ Iron and folate levels due to increased vitamin and mineral requirements
Endocrine system
Human placental lactogen (hPL): a hormone synthesized by syncytiotrophoblasts of the placenta, which promotes the production of insulin.
Increased maternal glucose levels: allows glucose to freely cross the placenta for consumption by the fetus for energy
Causes insulin resistance
Increased maternal proteolysis: provides a readily available supply of amino acids for the fetus
Increased maternal lipolysis: leads to increased free fatty acids and ketones to provide energy to the mother, preserving glucose and amino acids for the fetus
Gastrointestinal system
↑ Salivation
↓ Lower esophageal sphincter tone → gastroesophageal reflux
↓ Motility → constipation and bloating
Progesterone decreases colonic smooth muscle activity and decreases fasting MMCs (migrating myoelectric complex) in the small intestine
Gravid uterus mechanically impedes small intestine transit