Physiological changes during pregnancy

Hello friends!!! today we are going to talk about what happen physiologically during pregnancy
Striae gravidarum: “stretch marks” that develop in genetically predisposed women on the abdomen and buttocks

Spider angiomata and palmar erythema: caused by increased skin vascularity.

Chadwick sign: bluish or purplish discoloration of the vagina and cervix caused by increased skin vascularity.

Linea nigra: increased pigmentation of the lower abdominal midline from the pubis to the umbilicus.

Chloasma gravidarum: blotchy pigmentation of the nose and face(face mask)
2-Cardiovascular changes:

  • Arterial blood pressure: Systolic and diastolic values both decline early in the first trimester, reaching its lower level by 24–28 weeks and then gradually rising toward term (but never returning quite to prepregnancy baseline). Diastolic falls more than systolic, as much as 15 mm Hg. Arterial blood pressure is never normally elevated in pregnancy.
  • Venous blood pressure: Central venous pressure (CVP) is unchanged with pregnancy, but femoral venous pressure (FVP) increases two- to threefold by 30 weeks’ gestation.
  • Plasma volume: Plasma volume increases up to 50% with a significant increase by the first trimester. Maximum increase is by 30 weeks. This increase is even greater with multiple fetuses.
  • Systemic vascular resistance (SVR): SVR equals blood pressure (BP) divided by cardiac output (CO). Because BP decreases and CO increases, SVR declines by 30%, reaching its lower level by 20 weeks. This enhances uteroplacental perfusion.
  • Cardiac output (CO): CO increases up to 50%, with the major increase by 20 weeks. CO is the product of heart rate (HR) and stroke volume (SV), and both increase in pregnancy. HR increases by 20 beats/min by the third trimester. SV increases by 30% by the end of the first trimester.

CO is dependent on maternal position. 

CO is lowest in the supine position because of inferior vena cava compression resulting in decreased cardiac return.
CO is highest in the left lateral position.
CO increases progressively through the three stages of labor

  • Murmurs: A systolic ejection murmur along the left sternal border is normal in pregnancy, owing to increased CO passing through the aortic and pulmonary valves.

Diastolic murmurs are never normal in pregnancy and must be investigated.

  • Red blood cell (RBC) mass increases by 30% in pregnancy; thus, oxygen-carrying capacity increases. However, because plasma volume increases by 50% the calculated hemoglobin and hematocrit values decrease by 15%. The lower level of the hemoglobin value is at 28–30 weeks’ gestation. This is a physiologic dilutional effect, not a manifestation of anemia.
  • White blood cell (WBC) count increases progressively during pregnancy, with a mean value of up to 16,000/mm 3 in the third trimester.
  • Erythrocyte sedimentation rate (ESR) increases in pregnancy because of the increase in gamma globulins.
  • Platelet count normal reference range is unchanged in pregnancy.
  • Coagulation factors: Factors V, VII, VIII, IX, XII, and von Willebrand factor increase progressively in pregnancy, leading to a hypercoagulable state.
  • Stomach: Gastric motility decreases and emptying time increases from the progesteronen effect on smooth muscle. This increase in stomach residual volume, along with upward displacement of intraabdominal contents by the gravid uterus, predisposes to aspiration pneumonia with general anesthesia at delivery.
  • Large bowel: Colonic motility decreases and transit time increases from the progesterone effect on smooth muscle. This predisposes to increased colonic fluid absorption, resulting in constipation.
  • Tidal volume (Vt), the volume of air that moves in and out of the lungs at rest, increases with pregnancy to 40%. It is the only lung volume that does not decrease with pregnancy.
  • Minute ventilation (V̇e) increases up to 40% with the major increase by 20 weeks. V̇e is the product of respiratory rate (RR) and Vt. RR remains unchanged, with Vt increasing steadily throughout the pregnancy into the third trimester.
  • Residual volume (RV), the volume of air trapped in the lungs after deepest expiration, decreases up to 20% by the third trimester. This is largely due to the upward displacement of intraabdominal contents against the diaphragm by the gravid uterus.
  • Blood gases: The rise in Vt produces a respiratory alkalosis, with a decrease in Pco 2 from 40 to 30 mm Hg and an increase in pH from 7.40 to 7.45. An increased renal loss of bicarbonate helps compensate, resulting in an alkalotic urine.
  • The kidneys increase in size 1.5 cm because of the increase in renal blood flow; this hypertrophy does not reverse until three months postpartum.
  • Ureteral diameter increases owing to the progesterone effect on smooth muscle; the right side dilates more than the left in 90% of patients.
  • Glomerular filtration rate (GFR), renal plasma flow, and creatinine clearance all increase by 50% as early as the end of the first trimester; this causes a 25% decrease in serum blood urea nitrogen (BUN), creatinine, and uric acid.
  • Urine glucose normally increases; glucose is freely filtered and actively reabsorbed, although the tubal reabsorption threshold falls from 195 to 155 mg/dL.
  • Urine protein remains unchanged.

  • Pituitary size increases up to threefold due to lactotroph hyperplasia and hypertrophy, making it susceptible to ischemic injury (Sheehan syndrome) from postpartum hypotension.
  • Adrenal gland size is unchanged, but production of cortisol increases two- to threefold.
  • Thyroid size remains unchanged; thyroid binding globulin (TBG) increases,resulting in increased total T 3 and T 4 (although free T 3 and free T 4 remain unchanged).

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