From the Department's lecture slides, rewritten as a system-by-system table with the clinical meaning of each change. Know what is normal first, so you can spot what is not.
The reasoning chain: a hormone-driven, hyperdynamic state starts at conception and touches every organ → each change helps the mother carry the baby and prepare for blood loss at delivery → but each can also mimic disease (a murmur, a low haemoglobin, a glycosuria) or change how drugs behave. Resolve it by asking: is this the expected change, and is it in the expected range?
1. Why it matters on the ward
- Changes begin after conception and affect every system; most resolve after delivery with little residual effect in an uncomplicated pregnancy.
- They can confuse the examination (a systolic murmur, a displaced apex, pigmentation) and laboratory results (a lower haemoglobin, a higher ESR, a raised ALP), so you need pregnancy-specific reference ranges.
- They alter absorption, distribution, metabolism and elimination of drugs: more volume of distribution, faster kidney clearance, different liver handling.
2. Skin
| Change | Cause or note |
|---|---|
| Striae gravidarum (stretch marks) | Stretching in genetically predisposed women: abdomen, breasts, thighs, buttocks |
| Linea nigra | Pigmented line from the pubis to the umbilicus (MSH and oestrogen) |
| Chloasma (melasma) | Blotchy facial pigmentation |
| Spider naevi and palmar erythema | Raised oestrogen and skin blood flow; normal |
| Chadwick's sign | Bluish discolouration of vagina and cervix |
3. Cardiovascular system: a hyperkinetic state
| Parameter | Change | Why it matters |
|---|---|---|
| Blood pressure | Falls early; the diastolic falls more (up to 15 mmHg); lowest at 24–28 weeks; rises towards term but not above pre-pregnancy values | A raised BP is never normal: think pre-eclampsia |
| Plasma volume | Rises up to 50% (most by 30 weeks; more in twins) | A cushion against blood loss at delivery |
| Cardiac output | Rises up to 50% (most by 20 weeks) | Heart rate rises about 20 beats/min by the third trimester and stroke volume by about 30% |
| Systemic vascular resistance | Falls about 30% (lowest at 20 weeks) | Improves blood flow to the uterus and placenta |
| Central venous pressure | Unchanged | |
| Femoral venous pressure | Rises two- to threefold by 30 weeks | Leg oedema, varicose veins and haemorrhoids |
| Position | Cardiac output is lowest supine (the uterus compresses the inferior vena cava) and highest in left lateral | Supine hypotensive syndrome: examine and rest the woman tilted to the left |
The heart is enlarged and pushed up and to the left, so ECG and chest X-ray changes (left axis deviation, flattened T waves, a larger heart shadow) can look pathological.
Murmurs: a systolic ejection murmur along the left sternal border (increased output through the aortic and pulmonary valves), a third heart sound and a mammary soufflé are normal. Diastolic murmurs are never normal in pregnancy: investigate them (rheumatic mitral stenosis becomes dangerous in pregnancy because the heart rate and volume load rise).
4. Blood
| Parameter | Change | Meaning |
|---|---|---|
| Red cell mass | Rises about 30% | More oxygen carrying capacity |
| Haemoglobin and haematocrit | Fall about 15%, lowest at 28–30 weeks | Physiological (dilutional) anaemia: plasma rises more than red cells. The WHO cut-off for anaemia in pregnancy is 11 g/dL (10.5 g/dL in the second trimester) |
| White cells | Rise progressively; up to 16,000/mm³ in the third trimester (and far higher in labour) | Do not over-read a mild leucocytosis |
| ESR | Rises (more globulins and fibrinogen) | Useless as an infection marker in pregnancy |
| Platelets | The range is unchanged (can fall slightly: gestational thrombocytopenia) | |
| Clotting | Factors V, VII, VIII, IX, X, XII, von Willebrand factor and fibrinogen (doubles) rise; antithrombin III and protein S fall; fibrinolysis is reduced | A hypercoagulable state: protects against postpartum haemorrhage but raises the risk of venous thromboembolism |
| Immune system | T and B cell counts unchanged, function suppressed | More susceptible to malaria, viral infections, listeria and TB reactivation |
Iron: needs rise (about 1 g over pregnancy) and gastric acidity falls, so iron deficiency is common; supplement iron and folic acid routinely.
5. Respiratory system
The diaphragm rises about 4 cm and the chest widens; the subcostal angle broadens. Tidal volume rises about 40% and minute ventilation about 40%; residual volume falls; vital capacity and FEV1 are unchanged. The woman breathes faster in volume (not rate) and has a mild respiratory alkalosis (PaCO₂ about 30 mmHg, bicarbonate lower at about 20 mmol/L). Many women feel breathless (physiological dyspnoea) with no disease. Oxygen consumption rises about 20%. A PaCO₂ of 40 mmHg is abnormal in pregnancy and means respiratory failure is near.
6. Gastrointestinal system and liver
| Change | Cause | Result |
|---|---|---|
| Ptyalism, altered taste, increased appetite and thirst | Hormonal | Small frequent snacks help |
| Nausea and vomiting (about 50%) | hCG and oestrogen | Hyperemesis gravidarum is the severe form |
| Heartburn (reflux) | Relaxed lower oesophageal sphincter (progesterone, relaxin) and a pressing uterus | Antacids, small meals, head-up sleeping |
| Constipation | Reduced motility (progesterone) and more water absorption | Fibre and fluids |
| Reduced gastric acidity | Interferes with iron absorption | |
| Gallbladder | Larger, empties slowly; cholestasis is almost physiological | Gallstones and intrahepatic cholestasis of pregnancy |
| Liver tests | Albumin falls, ALP rises (placental), globulins, fibrinogen and binding proteins rise; ALT and AST stay normal | Raised ALT/AST is abnormal: HELLP, fatty liver, hepatitis |
7. Urinary system
The kidneys enlarge slightly; the renal pelvis and ureters dilate (more on the right) from progesterone relaxing smooth muscle and from pressure at the pelvic brim. Renal plasma flow rises about 50–80% and GFR about 50%, so serum creatinine falls (a creatinine above 75 µmol/L (0.8 mg/dL) should raise concern) and urea falls. Glycosuria (reduced tubular reabsorption) and mild proteinuria (up to 300 mg/day) can be normal. Frequency and nocturia are common; urinary stasis explains the high risk of pyelonephritis, so screen for asymptomatic bacteriuria.
8. Endocrine system
| Gland | Change |
|---|---|
| Pituitary | Anterior pituitary enlarges (prolactin rises); oxytocin released in labour |
| Thyroid | Enlarges slightly (a "physiological goitre"); thyroid-binding globulin doubles, so total T3 and T4 rise but free T3 and T4 do not; most women are euthyroid; hCG can mildly stimulate the thyroid in early pregnancy |
| Parathyroid | More active to meet calcium needs |
| Adrenal | Total cortisol rises; free cortisol is unchanged; aldosterone rises (salt and water retention) |
| Pancreas | Insulin resistance rises in the second and third trimesters (human placental lactogen), the basis of gestational diabetes |
Placental hormones
- hCG: made by the trophoblast; peaks at 8–12 weeks; keeps the corpus luteum producing progesterone until the placenta takes over (about 8–10 weeks).
- Progesterone: first from the corpus luteum, then the placenta (output about 250 mg/day at term). It relaxes smooth muscle (less gut, bladder and ureteric tone: constipation, reflux, urinary stasis), dilates veins, lowers diastolic pressure, raises body temperature and drives nausea; it maintains the pregnancy and prevents uterine contractions.
- Oestrogens: from the ovary early, then the placenta (oestriol about 85%, rising up to term; oestriol needs the fetal adrenal and liver). They grow the uterus, develop the breasts (with progesterone), soften connective tissue, cause water and sodium retention.
- Human placental lactogen (hPL): anti-insulin, shifts energy to the fetus.
- Relaxin: loosens pelvic ligaments.
9. Reproductive system
| Organ | Change |
|---|---|
| Uterus | Hypertrophy and hyperplasia. Length rises from 7.5 cm to about 35 cm and weight from about 50 g to 1,000 g at term; capacity from about 10 mL to 5 L. Dextrorotation (tilted and twisted to the right in about 80%). Lower uterine segment forms from the isthmus from about the fourth month and reaches about 10 cm at term |
| Cervix | Softens (Goodell's sign), oedematous and congested; glands multiply and secrete a thick mucus plug (operculum) that closes the canal |
| Vagina and vulva | Increased vascularity, soft, moist, bluish (Chadwick's sign); varicosities; increased discharge with lower pH |
| Ovary | One contains the corpus luteum of pregnancy; no ovulation during pregnancy |
| Pelvic ligaments and joints | Relax (relaxin), so the pelvis becomes more mobile and the capacity increases; backache and pubic pain |
| Breasts | Increased size, vascularity, warmth and tenderness; darker nipples and areola, secondary areola, Montgomery's tubercles; colostrum by the end of the third month |
10. Metabolism, weight and the musculoskeletal system
- Weight gain averages 10–12 kg (about 0.4 kg a week in the second and third trimester); more than 1 kg a week is abnormal (fluid retention).
- Basal metabolic rate rises about 15–20%; calorie needs rise about 300 kcal a day in the second and third trimester.
- Fasting glucose falls (the fetus uses it), post-meal glucose rises; cholesterol and triglycerides rise.
- The centre of gravity shifts: lordosis, backache, a waddling gait.
11. Clinical pearls
- Hb of 10.5–11 g/dL at 30 weeks may be dilutional; do iron studies and treat deficiency, but do not transfuse for physiological anaemia.
- A diastolic murmur is always abnormal. A soft systolic murmur is normal.
- BP of 130/80 or more in the second trimester is not "normal for pregnancy": check urine protein and think pre-eclampsia.
- A normal pregnancy PaCO₂ is about 30 mmHg. "Normal" 40 mmHg may be a warning.
- Glycosuria alone does not mean diabetes in pregnancy; do a glucose tolerance test.
- Women are hypercoagulable: think DVT and PE in a woman with a swollen calf or chest pain.
Examiner questions
- Describe the cardiovascular changes of pregnancy and their clinical effects.
- Why does a pregnant woman have a "low" haemoglobin, and at what level do you call it anaemia?
- What is the supine hypotensive syndrome and how do you prevent it?
- Which hormones maintain pregnancy and what does each do?
Practice questions
1. By term, plasma volume has risen by about: A. 10% · B. 20% · C. 30% · D. 50% · E. 100% Answer: D. The red cell mass rises only about 30%, so the haemoglobin concentration falls.
2. Which murmur is NOT normal in pregnancy? A. A soft systolic ejection murmur · B. A mammary soufflé · C. A third heart sound · D. An early diastolic murmur · E. A venous hum Answer: D.
3. Which change in pregnancy explains the tendency to heartburn? A. Increased gastric acid · B. Relaxation of the lower oesophageal sphincter by progesterone · C. Reduced saliva · D. Increased gastric emptying · E. Reduced intra-abdominal pressure Answer: B.
4. Which statement about thyroid hormones in pregnancy is TRUE? A. Free T4 doubles · B. Total T4 rises because thyroid-binding globulin doubles, while free T4 is unchanged · C. TSH is always high · D. Most women are hypothyroid · E. Total T4 falls Answer: B.
5. At term the uterus weighs about: A. 100 g · B. 300 g · C. 500 g · D. 1,000 g · E. 2,500 g Answer: D.