Physiology changes during pregnancy mbbs obstetrics

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Physiological changes during pregnancy - MBBS obstetrics topic map

General and metabolic
- Weight gain, basal metabolic rate, water retention
- Carbohydrate, protein, fat, calcium and iron metabolism
Cardiovascular system
- Increased blood volume, cardiac output and heart rate
- Reduced systemic vascular resistance and physiological fall in blood pressure
- Venous stasis, edema and supine hypotensive syndrome
Hematological system
- Physiological anemia due to hemodilution
- Increased leukocyte count
- Hypercoagulable state and changes in clotting factors
Respiratory system
- Diaphragmatic elevation and changes in lung volumes
- Increased tidal volume and minute ventilation
- Physiological respiratory alkalosis
Renal and urinary system
- Increased renal plasma flow and GFR
- Reduced serum creatinine and urea
- Hydroureter, hydronephrosis, glycosuria and frequency of micturition
Gastrointestinal system
- Nausea and vomiting, reflux, reduced gut motility, constipation
- Gallbladder stasis and altered liver-related laboratory values
Endocrine system
- Pituitary, thyroid, adrenal and pancreatic adaptations
- Insulin resistance in late pregnancy and diabetogenic state
Reproductive organs and breasts
- Uterine enlargement and increased uteroplacental blood flow
- Cervical softening, vaginal changes, breast enlargement and colostrum
Musculoskeletal and skin
- Lordosis, ligament laxity, diastasis recti
- Linea nigra, chloasma, striae gravidarum
Nervous system and eyes

Sleep and mood changes, carpal tunnel symptoms
Minor visual and intraocular pressure changes

High-yield principle: pregnancy produces increased circulatory volume and cardiac output, increased ventilation and GFR, plus hemodilution, hypercoagulability, and progressive insulin resistance. These are physiological adaptations, but they can resemble disease if interpreted without pregnancy-specific reference ranges.

Which section would you like as a detailed exam-oriented note: 1) cardiovascular and hematological, 2) respiratory and renal, 3) endocrine and metabolic, or 4) complete system-wise short note with a revision table?

Create a complete MBBS revision table of these changes

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physiological changes in pregnancy cardiovascular renal respiratory hematologic reference values review

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Physiological changes during pregnancy: MBBS revision table

System	Normal physiological change	Important values / mechanism	Clinical relevance
Weight and body water	Weight increases; total body water and extracellular fluid increase	Average total weight gain in a normal BMI pregnancy: 11.5-16 kg. Plasma volume and interstitial fluid both expand.	Dependent ankle edema can be normal. Sudden generalized edema with hypertension/proteinuria needs evaluation.
Basal metabolic rate	Increases progressively	About 15-20% increase near term due to fetal, placental and maternal metabolic demands.	Heat intolerance, sweating and increased appetite may occur.
Cardiovascular: blood volume	Blood volume rises substantially	Plasma volume increases from 6-8 weeks, reaches maximum at about 32 weeks. Increase is about 45% or 1200-1600 mL. Red-cell mass rises only 20-30%. Creasy & Resnik's Maternal-Fetal Medicine, p. 208.	Prepares for blood loss at delivery but causes dilutional anemia.
Cardiovascular: cardiac output	Cardiac output increases	Increases by about 30-50%, mainly from increased stroke volume early in pregnancy and increased heart rate later. Peak is around 20-28 weeks.	A flow systolic murmur, bounding pulse and mild tachycardia may be physiological. Cardiac disease may worsen because of increased circulatory load.
Heart rate	Resting pulse rises	About 10-20 beats/minute above non-pregnant values.	Persistent marked tachycardia requires exclusion of anemia, infection, hyperthyroidism, arrhythmia or cardiac disease.
Stroke volume	Increases	About 20-30% increase.	Contributes to increased cardiac output.
Systemic vascular resistance	Falls	Decreases by about 25-30% because progesterone, nitric oxide and other vasodilatory influences reduce vascular tone.	Causes the normal fall in BP during mid-pregnancy.
Blood pressure	Falls in early to mid-pregnancy, then returns toward baseline near term	Diastolic BP falls more than systolic BP, usually by about 10 mmHg; nadir around 20-24 weeks.	Hypertension is not a normal finding in pregnancy.
Venous system	Venous pressure in lower limbs rises; venous return from legs is impeded	Enlarging uterus compresses pelvic veins and, when supine, the inferior vena cava.	Varicose veins, hemorrhoids and dependent edema may occur. Avoid prolonged supine posture in late pregnancy.
Supine hypotensive syndrome	Hypotension when lying supine in late pregnancy	Aortocaval compression reduces venous return, cardiac output and uteroplacental perfusion.	Symptoms: dizziness, pallor, sweating, nausea, hypotension. Treat by placing the woman in the left lateral position.
Cardiac examination	Position and sounds alter	Heart is displaced upward and leftward by the elevated diaphragm. Soft ejection systolic flow murmur is common; S1 may be louder and an S3 may be heard.	Diastolic murmurs, a loud persistent systolic murmur, cyanosis, syncope or heart-failure signs are abnormal.
ECG	Minor changes may occur	Left-axis shift; small Q wave and T-wave inversion in lead III; occasional ectopics may occur.	Interpret with pregnancy context.
Hematology: hemoglobin and hematocrit	Physiological hemodilution	Plasma-volume expansion exceeds red-cell mass expansion, so Hb and hematocrit fall. This is most evident in late second and early third trimester.	Physiological anemia of pregnancy. Hb below 11 g/dL in first/third trimester or below 10.5 g/dL in second trimester generally warrants assessment for iron deficiency and other causes.
Hematology: leukocytes	Leukocytosis	WBC count rises, mainly neutrophils. It may rise further during labor and immediately postpartum.	Mild leukocytosis alone does not diagnose infection.
Platelets	Mild fall may occur	Gestational thrombocytopenia can produce a mildly reduced platelet count, usually without bleeding.	Significant thrombocytopenia needs evaluation for pre-eclampsia/HELLP, immune thrombocytopenia, infection and other causes.
Coagulation	Hypercoagulable state	Fibrinogen and factors VII, VIII, IX, X and XII increase; protein S decreases; fibrinolysis decreases.	Protects against postpartum hemorrhage but raises risk of venous thromboembolism, especially postpartum.
Respiratory: anatomy	Diaphragm elevates	Upward displacement by about 4 cm, with increased transverse chest diameter.	Chest radiograph may show an elevated diaphragm without disease.
Tidal volume	Increases	About 30-40% increase, mainly progesterone-mediated.	Produces a feeling of breathlessness despite normal oxygenation.
Minute ventilation	Increases	Increases by about 40-50%, predominantly because of increased tidal volume. Respiratory rate changes little or increases slightly.	Mild dyspnea is common and physiological if there is no hypoxia, wheeze, chest pain or marked limitation.
Oxygen consumption	Increases	Approximately 20% increase at term.	Reduced reserve makes hypoxia develop more rapidly during apnea or severe respiratory illness.
Functional residual capacity	Decreases	Falls by about 20% because expiratory reserve volume and residual volume decrease.	Greater risk of rapid desaturation during anesthesia or respiratory compromise.
Lung function tests	Mostly unchanged	FEV1, FVC and peak expiratory flow are usually unchanged.	A reduced PEFR in a woman with asthma should not be attributed to pregnancy.
Acid-base status	Chronic compensated respiratory alkalosis	Progesterone increases respiratory drive. PaCO₂ falls to about 28-32 mmHg; serum bicarbonate falls to about 18-22 mmol/L; pH is mildly increased.	A PaCO₂ of 40 mmHg may indicate relative hypoventilation in a pregnant patient. Normal pregnancy respiratory values are summarized in this review of pregnancy physiology.
Renal: kidney size and collecting system	Kidneys enlarge slightly; ureters and renal pelvis dilate	Progesterone relaxes smooth muscle; uterus contributes to mechanical compression. Dilatation is usually greater on the right.	Physiological hydroureter/hydronephrosis predisposes to urinary stasis and UTI.
Renal plasma flow and GFR	Both increase early	Renal plasma flow rises by about 50-80% and GFR by about 40-50%.	Serum creatinine, urea and uric acid are lower than non-pregnant values. A "normal" non-pregnant creatinine can be abnormal in pregnancy.
Urinary findings	Frequency, nocturia and mild glycosuria may occur	Increased GFR raises filtered glucose load; tubular reabsorption may be relatively inadequate.	Glycosuria alone does not diagnose diabetes, but screening for gestational diabetes is still required. Proteinuria is not considered normal if significant.
Sodium and water handling	Sodium and water retention	Activation of renin-angiotensin-aldosterone system with resetting of osmoreceptors lowers plasma osmolality.	Mild hyponatremia may be physiological.
Gastrointestinal: nausea/vomiting	Common, especially in the first trimester	Related to hCG, estrogen and progesterone effects.	Severe vomiting, dehydration, weight loss or ketonuria suggests hyperemesis gravidarum.
Gastrointestinal: lower esophageal sphincter	Tone decreases	Progesterone relaxes smooth muscle; raised intra-abdominal pressure contributes late in pregnancy.	Gastroesophageal reflux and heartburn are common.
Gastrointestinal: bowel motility	Gastric emptying and intestinal transit slow	Progesterone-mediated smooth-muscle relaxation.	Constipation, bloating and increased risk of aspiration during anesthesia.
Gallbladder	Emptying is delayed	Increased residual gallbladder volume and bile stasis occur.	Predisposes to biliary sludge and gallstones.
Liver	Most liver tests remain normal; some alter physiologically	Alkaline phosphatase rises due to placental production. Albumin and total protein fall due to hemodilution. AST, ALT and bilirubin should generally remain within normal limits.	Raised transaminases or bilirubin should not be dismissed as a normal pregnancy change.
Endocrine: pituitary	Pituitary enlarges	Lactotroph hyperplasia causes increased prolactin.	Prolactin prepares breast for lactation. Pituitary enlargement can make the gland more vulnerable in severe postpartum hemorrhage.
Thyroid	Total T4 and T3 increase; TBG increases	Estrogen increases thyroxine-binding globulin. hCG has weak TSH-like action, so TSH may be lower in the first trimester.	Use trimester-specific reference ranges. Total T4 alone can be misleading.
Endocrine: cortisol	Total cortisol rises	Increased cortisol-binding globulin and increased adrenal activity.	Pregnancy is a state of relative hypercortisolism.
Endocrine: insulin and glucose	Progressive insulin resistance, especially after mid-pregnancy	Human placental lactogen, placental growth hormone, cortisol, progesterone and prolactin antagonize insulin action. Fasting glucose tends to be lower; postprandial glucose may rise.	Pregnancy is a diabetogenic state. Gestational diabetes commonly becomes apparent in the second half of pregnancy.
Lipid metabolism	Hyperlipidemia	Triglycerides, total cholesterol and lipoproteins rise, especially in the third trimester.	Physiological, but marked elevation with symptoms may need evaluation for pancreatitis risk.
Protein metabolism	Increased protein requirement	Protein is required for maternal tissues, fetus, placenta and expanded blood volume.	Low serum albumin partly reflects hemodilution, not necessarily malnutrition or liver disease.
Calcium metabolism	Total serum calcium falls but ionized calcium remains essentially unchanged	Fall in albumin lowers measured total calcium. Intestinal calcium absorption rises.	Assess corrected calcium or ionized calcium if a calcium disorder is suspected.
Iron metabolism	Iron demand rises markedly	About 1000 mg total iron requirement during pregnancy: approximately 500 mg for maternal red-cell expansion, 300 mg for fetus/placenta, and 200 mg for obligatory losses. Creasy & Resnik's Maternal-Fetal Medicine, p. 208.	Iron supplementation is commonly needed to prevent iron-deficiency anemia.
Musculoskeletal	Lordosis, widened gait and pelvic-joint laxity	Relaxin and progesterone contribute to ligamentous laxity; center of gravity shifts forward.	Backache, pelvic discomfort and carpal tunnel symptoms are common.
Abdominal wall	Diastasis recti may develop	Separation of rectus abdominis muscles due to uterine enlargement.	Usually benign; support and postnatal rehabilitation may help.
Breasts	Enlargement, tenderness, pigmentation and colostrum	Estrogen promotes ductal growth; progesterone promotes lobuloalveolar development; prolactin prepares for milk synthesis.	Colostrum may be expressed late in pregnancy.
Uterus	Major enlargement and increased blood flow	Uterine blood flow rises greatly, reaching about 500-750 mL/min at term.	Uterus is palpable above the symphysis pubis at about 12 weeks and reaches the umbilicus around 20 weeks.
Cervix and vagina	Softening, vascularity and increased discharge	Cervical softening: Goodell sign. Bluish vaginal/cervical discoloration: Chadwick sign. Increased vaginal discharge occurs.	Leukorrhea is usually normal if non-offensive and without itching or irritation.
Skin	Pigmentation and connective-tissue changes	Linea nigra, chloasma/melasma, areolar darkening, striae gravidarum, spider angiomas and palmar erythema may occur.	Pruritus with jaundice, severe rash or generalized itching needs evaluation.
Nervous system	Sleep disturbance, altered mood, carpal tunnel symptoms	Fluid retention can compress the median nerve; mechanical and hormonal changes contribute.	Severe persistent headache, visual symptoms, seizures or focal deficits are not normal.
Eye	Corneal thickness/curvature change and intraocular pressure decreases	Fluid retention and hormonal effects.	Contact-lens intolerance can occur. Persistent visual disturbance warrants evaluation, particularly for pre-eclampsia.
Immunity	Immune response is modified, not simply suppressed	Shift in immune regulation supports fetal tolerance while retaining antimicrobial defense.	Some autoimmune diseases improve while others may worsen. Infection assessment remains important.

Last-minute numbers to remember

Parameter	Typical change in pregnancy
Plasma volume	↑ 45%
Red-cell mass	↑ 20-30%
Cardiac output	↑ 30-50%
Heart rate	↑ 10-20/min
Systemic vascular resistance	↓ 25-30%
Diastolic BP	↓ about 10 mmHg in mid-pregnancy
GFR	↑ 40-50%
Tidal volume	↑ 30-40%
Minute ventilation	↑ 40-50%
Functional residual capacity	↓ about 20%
PaCO₂	28-32 mmHg
Serum HCO₃⁻	18-22 mmol/L
Oxygen consumption	↑ about 20%

Exam line

Pregnancy is characterized by hypervolemia, increased cardiac output, physiological hemodilution, hypercoagulability, increased GFR, chronic compensated respiratory alkalosis, and progressive insulin resistance.

The cardiovascular, respiratory, renal and hematological numerical changes above align with a clinical physiology review and the cited obstetric textbook section.

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