Physiological Changes in Pregnancy

What is the primary vascular change in pregnancy, and how does it affect blood pressure?

Systemic vasodilation. BP drops early, reaches its lowest point at 22-24 weeks, and returns to pre-pregnancy levels at term. Exam Trap: BP never normally increases above pre-pregnancy levels in a healthy pregnancy.

How much does Cardiac Output (CO) increase during pregnancy, and when does it peak?

CO increases by about 40%, peaking around 20-28 weeks. This is mostly driven by an increase in stroke volume and a minimal increase in heart rate.

Which heart murmurs and heart sounds are considered normal (physiological) in a pregnant woman?

Systolic murmurs and an S3 gallop are normal due to increased blood volume and cardiac output. Exam Trap: Diastolic murmurs are always abnormal and require further evaluation!

What is the correct maternal position for measuring blood pressure, and why?

Sitting or lying with a 30-degree tilt. Supine positioning should be avoided due to "Supine Hypotension Syndrome," where the gravid uterus compresses the IVC, decreasing venous return.

What normal ECG changes might be seen in a pregnant woman?

Left ventricular hypertrophy, inverted T-waves in lead III, and Q-waves in lead III. Exam Trap: ST-elevation is NOT a normal finding.

Explain the mechanism of "physiologic anemia" of pregnancy.

Plasma volume increases massively (40-50%). Erythrocyte (RBC) production also increases (20-30%), but proportionally less than the plasma volume. This causes hemodilution (a dilutional drop in hemoglobin/hematocrit).

How do maternal leukocyte (WBC) counts and the Erythrocyte Sedimentation Rate (ESR) change?

Leukocytes (mainly polymorphonuclear neutrophils) increase. ESR is also normally elevated due to increased fibrinogen. Exam Tip: Because ESR naturally rises, it cannot be used as an inflammatory marker in pregnancy; use CRP instead.

Which specific coagulation factors increase, creating a hypercoagulable state in pregnancy?

Factors II (Prothrombin), VII, VIII, IX, X, XII, and Fibrinogen all INCREASE.

Which coagulation factors and anticoagulants decrease during pregnancy?

Factor XI decreases. Endogenous anticoagulants (Protein S, Antithrombin III) and overall fibrinolytic activity DECREASE.

What drives the 40-50% increase in minute ventilation during pregnancy, and which parameter changes the most?

It is triggered by progesterone. The increase is almost entirely due to an increased Tidal Volume (TV). The Respiratory Rate (RR) is only minimally increased or unchanged.

What changes occur in maternal arterial blood gas (ABG) values during pregnancy?

Progesterone-driven hyperventilation leads to a reduction in PaCO2 (falls to ~30 mmHg), causing a compensated respiratory alkalosis. The kidneys compensate by excreting more bicarbonate (HCO3 falls).

How do GFR and Renal Plasma Flow (RPF) change during pregnancy, and how does this affect kidney labs?

GFR increases by 50% and RPF increases by 60-80%. Because of this increased filtration, serum creatinine and urea (BUN) levels normally FALL.

Why do pregnant women often develop mild-moderate hydronephrosis, and on which side is it more prominent?

Smooth muscle relaxation (via progesterone) and mechanical uterine compression cause ureter dilation. It is more marked on the RIGHT side due to the dextrorotation of the gravid uterus. Exam Trap: Left-sided dominance is a false statement.

What is the normal upper limit of acceptable protein excretion in the urine of a pregnant woman?

Up to 300 mg/day (compared to 150 mg/day in non-pregnant individuals) is accepted due to the "leaky" hyper-filtering kidneys.

What causes the common GI symptoms of GERD, delayed gastric emptying, and constipation?

Progesterone causes widespread smooth muscle relaxation, leading to decreased lower esophageal sphincter pressure and decreased gut peristalsis (increased transit time).

Which liver function tests remain normal, and which significantly elevate during pregnancy?

AST, ALT, and Bilirubin remain NORMAL (or slightly fall). Alkaline Phosphatase (Alk Phos) is elevated 2-4 times due to placental production and smooth muscle relaxation of the gallbladder.

Why does total maternal serum albumin and total protein concentration decrease?

Due to hemodilution (the massive increase in plasma volume). The liver increases protein synthesis to try and keep up, but the concentration still falls.

Describe the changes in insulin resistance and maternal glucose metabolism during pregnancy.

Pregnancy is a state of relative insulin resistance (caused by anti-insulin placental hormones like hPL, cortisol, and progesterone) to ensure glucose is spared for the fetus.

When does the "accelerated starvation state" occur in pregnancy?

Late in pregnancy (not the first few weeks!). The mother's metabolism shifts toward utilizing fat stores for energy, resulting in increased ketone production and clearance.

Why might pregnant women experience transient hyperthyroidism in the first trimester, and what condition is this associated with?

The beta-subunit of hCG strongly resembles TSH, stimulating the thyroid to release free T4 and suppress TSH. This is biochemically associated with severe morning sickness / Hyperemesis Gravidarum.

How does pregnancy affect Total T4, Total T3, and Free T4/T3?

Total T4 and Total T3 increase because estrogen drives a rise in Thyroid Binding Globulin (TBG). However, the physiologically active Free T4 and Free T3 remain relatively CONSTANT.

Describe the changes in Calcium metabolism (Total Calcium, Ionized Calcium, and PTH).

Total calcium declines (due to hemodilution of albumin). Ionized (free/active) calcium remains UNCHANGED. PTH decreases or remains low-normal in early pregnancy due to increased calcitriol (Vitamin D) absorption. Exam Trap: PTH does not routinely increase early on.

What happens to the size of the anterior pituitary, and what complication does this pose?

The anterior pituitary increases in volume by up to 35% (lactotrophs multiply). This high metabolic demand without a proportional increase in blood supply makes it highly vulnerable to infarction/necrosis if the mother suffers massive postpartum hemorrhage (Sheehan's Syndrome).

What hormones drive the skin pigmentation changes in pregnancy (e.g., melasma, linea nigra), and what are the classic vascular skin findings?

Increased Melanocyte Stimulating Hormone (MSH) causes hyperpigmentation. Increased estrogen causes vascular changes like spider nevi and palmar erythema (both are normal).

How can you tell the difference between old and new striae gravidarum (stretch marks)?

New striae (from current pregnancy breakage and inflammation) are pink. Old striae (from previous pregnancies) are white/silver.

How much does Total Body Water increase in normal pregnancy, and what is the average normal weight gain?

Total body water increases by 6-8 Liters. The average normal gestational weight gain is 12.5 kg. Exam Trap: An option stating total body water only increases by 3 Liters is false.