Maternal Changes in Pregnancy - 5 Marks Exam Answer

Introduction

1. CARDIOVASCULAR CHANGES

• Cardiac output rises due to increases in both heart rate and stroke volume. The greatest rise occurs during labor and immediately after delivery.
• Blood volume increases by 1000-1500 mL by term (total ~90 mL/kg), enabling the mother to tolerate blood loss at delivery (average 200-500 mL vaginally; 800-1000 mL at C-section).
• Plasma volume increases more (55%) than red cell mass (45%) - this produces dilutional (physiological) anemia of pregnancy. Hemoglobin remains >11 g/dL normally.
• Systemic vascular resistance falls from the first trimester (nadir in mid-second trimester) due to progesterone-mediated vasodilation and the low-resistance uteroplacental circuit.
• Aortocaval compression (Supine Hypotension Syndrome): After 20 weeks, the gravid uterus can compress the inferior vena cava in the supine position, reducing venous return and causing hypotension, pallor, sweating, and nausea - seen in ~5% of women. Managed by left lateral tilt (>15 degrees wedge under right hip).
• Electrocardiogram changes: Diaphragm elevation shifts the heart leftward, causing left axis deviation, T-wave changes, and apparent cardiomegaly on chest X-ray.
• Murmurs: A systolic ejection murmur (grade I-II) is heard in most pregnant women due to increased flow across the aortic and pulmonary valves - this is normal. Third and fourth heart sounds may also appear.

2. RESPIRATORY CHANGES

• Minute ventilation increases 50% (mainly due to tidal volume increase). This is driven by elevated progesterone, which stimulates the respiratory center directly.
• Physiological hyperventilation causes a mild respiratory alkalosis (PaCO2 falls to 28-32 mmHg). This is compensated by renal bicarbonate excretion (HCO3 falls to ~20 mEq/L) - so pH is only mildly elevated.
• The P50 of hemoglobin increases (27 to 30 mmHg) due to elevated 2,3-DPG, facilitating oxygen unloading to fetal tissues.
• FRC decreases 20% at term due to uterine elevation of the diaphragm reducing expiratory reserve volume.
• The combination of decreased FRC + increased O2 consumption means pregnant women desaturate very rapidly during apnea - hence mandatory pre-oxygenation before general anesthesia.
• Upper airway: Mucosal edema, vascular engorgement, and capillary congestion of the respiratory mucosa predisposes to bleeding and obstruction. Smaller endotracheal tubes (6-6.5 mm) should be used.
• The diaphragm rises ~4 cm, but chest anteroposterior diameter increases to compensate. Vital capacity is minimally affected.

3. HEMATOLOGICAL CHANGES

• Dilutional anemia: Plasma volume rises more than RBC mass, causing Hb to fall but remain >11 g/dL.
• Hypercoagulable state: Fibrinogen and Factors VII, VIII, IX, X, XII all increase (+30 to 250%). Factor XI may decrease. This is protective against hemorrhage at delivery but predisposes to DVT.
• Leukocytosis: WBC rises to as high as 21,000/μL in the third trimester (physiological).
• Platelets: Mild decrease (~10%) due to dilution and increased consumption.
• Iron and folate deficiency anemia can develop due to fetal utilization - supplementation is essential.
• Fibrinolysis accelerates late in the third trimester.

4. RENAL CHANGES

• GFR increases 50% due to increased renal plasma flow and cardiac output. So normal creatinine and BUN values are lower in pregnancy - a creatinine of 1.0 mg/dL (normal in non-pregnant) may indicate renal impairment in a pregnant woman.
• Glycosuria (1-10 g/day) is common and physiological - due to reduced tubular threshold for glucose.
• Mild proteinuria (<300 mg/day) is normal; >300 mg/day raises concern for preeclampsia.
• Plasma osmolality decreases by 8-10 mOsm/kg.
• Hydronephrosis and hydroureter (more common on the right) occur due to uterine compression and progesterone-induced smooth muscle relaxation.

5. GASTROINTESTINAL CHANGES

• Gastric emptying is delayed from early pregnancy. Progesterone relaxes smooth muscle throughout the GI tract.
• Lower esophageal sphincter (LES) tone decreases due to progesterone + mechanical upward displacement of the stomach by the uterus. This causes:
  • Gastroesophageal reflux (heartburn - very common)
  • High risk of regurgitation and pulmonary aspiration during anesthesia (Mendelson's syndrome)
• Constipation is common due to reduced gut motility.
• Gallstones: Elevated progesterone inhibits cholecystokinin release, causing incomplete gallbladder emptying. Together with altered bile composition, this predisposes to cholesterol gallstone formation.

6. HEPATIC CHANGES

• Overall hepatic function and blood flow are unchanged.
• Mild elevations in serum transaminases and LDH in third trimester.
• Serum alkaline phosphatase elevated - due to placental secretion (not hepatic disease).
• Serum albumin decreases (dilutional) - reduces colloid oncotic pressure and affects drug protein binding.
• Pseudocholinesterase activity decreases 25-30% at term - clinical significance for succinylcholine metabolism is minimal but may prolong action. Does not return to normal until 6 weeks postpartum.

7. CNS CHANGES

• MAC (minimum alveolar concentration) decreases 40% by term for all volatile anesthetic agents - due to elevated progesterone (sedating effect) and β-endorphin surge.
• Sensitivity to local anesthetics increases - neural blockade occurs at reduced concentrations (MLAC reduced ~30% for epidural anesthesia). This is hormonally mediated and also due to epidural venous engorgement.
• Engorged epidural veins reduce epidural space volume, increasing cephalad spread of spinal/epidural blocks.

8. METABOLIC AND ENDOCRINE CHANGES

• Insulin resistance increases (diabetogenic state) due to placental secretion of human placental lactogen (hPL/human chorionic somatomammotropin). Insulin levels rise progressively. Pancreatic beta cells undergo hyperplasia.
• Gestational diabetes mellitus (GDM) can occur in susceptible women.
• Thyroid: Thyroid gland hypertrophies; thyroid-binding globulin increases (due to hCG and estrogens), so total T3 and T4 levels rise, but free T3 and T4 remain normal - pregnancy is a euthyroid state.
• Calcium metabolism: Parathyroid hormone and 1,25-dihydroxyvitamin D3 increase to support fetal skeletal development.
• Adrenal changes: Cortisol levels rise with elevated corticosteroid-binding globulin.

9. SKIN AND MUSCULOSKELETAL CHANGES

• Pigmentation increases (chloasma/melasma - "mask of pregnancy," linea nigra) due to elevated MSH and estrogens.
• Striae gravidarum - stretch marks on abdomen, breasts, thighs due to skin stretching and cortisol effects on collagen.
• Spider angiomas and palmar erythema - due to elevated estrogens causing vascular dilation.
• Edema is common, especially in the lower limbs (venous stasis from IVC compression).
• Relaxin hormone loosens ligaments, especially in the pelvis (pubic symphysis, sacroiliac joints) to facilitate delivery. Can cause lower back pain and gait changes.

Quick Summary Table for Exam

Vaccination During Pregnancy - Indications and Types (5 Marks Exam Answer)

Introduction

• Inactivated vaccines / toxoids / subunit vaccines = generally SAFE
• Live attenuated vaccines = generally CONTRAINDICATED (risk of fetal infection)

CLASSIFICATION OF VACCINES IN PREGNANCY

A. ROUTINELY RECOMMENDED DURING EVERY PREGNANCY

1. Tdap (Tetanus, Diphtheria, Acellular Pertussis)

• Neonatal/infant pertussis (whooping cough) is a major killer in the first 2 months of life - before the infant can be vaccinated.
• Administering Tdap at 27-36 weeks maximizes the transplacental transfer of maternal IgG antibodies to the fetus before delivery.
• The earlier in the 27-36 week window, the more antibody reaches the neonate.
• If not given during pregnancy, Tdap should be administered immediately postpartum (to at least protect via cocooning strategy).
• Household contacts and caregivers of newborns who have not previously received Tdap should also be vaccinated ("cocoon strategy").

2. Inactivated Influenza Vaccine (IIV) / Recombinant Influenza Vaccine (RIV)

• Pregnant women are at high risk of severe influenza complications (pneumonia, hospitalization, preterm labor) due to physiological immunosuppression, altered cell-mediated immunity, and pulmonary changes.
• Maternal IgG crosses the placenta and protects the newborn for the first 6 months (until the infant can be vaccinated).
• Live attenuated influenza vaccine (LAIV) is given intranasally and is CONTRAINDICATED in pregnancy.
• Only inactivated or recombinant influenza vaccines are safe.

3. COVID-19 Vaccine

• Pregnant women are at significantly increased risk of severe COVID-19 including ICU admission, mechanical ventilation, preterm birth, and maternal death.
• mRNA vaccines have been confirmed safe in pregnancy through large real-world data (no increased risk of miscarriage, preterm birth, or congenital anomalies).
• Maternal IgG is transferred to the neonate.
• ACOG, CDC, WHO, and AAP all recommend COVID-19 vaccination during pregnancy.

4. RSV (Respiratory Syncytial Virus) Vaccine - Abrysvo (Pfizer)

• RSV is the leading cause of bronchiolitis and lower respiratory tract disease in infants under 6 months.
• Maternal vaccination transfers RSV-specific IgG to the fetus, protecting the neonate in the first months of life.
• Alternative approach: infant administration of nirsevimab (a long-acting monoclonal antibody) at birth - used when maternal vaccination was not given.
• Timing is restricted to the RSV season window to optimize protection during the infant's most vulnerable period.

B. RECOMMENDED FOR SPECIFIC INDICATIONS (Not All Pregnancies)

5. Hepatitis B Vaccine (HepB)

• Prevents mother-to-child transmission of HBV.
• HBV infection during pregnancy increases risk of preterm birth, low birth weight, and vertical transmission to the neonate (especially during delivery).
• Safe in all trimesters.

6. Hepatitis A Vaccine (HepA)

7. Meningococcal Vaccines (MenACWY, MenB)

• MenACWY: May be given if indicated.
• MenB: Pregnancy is a precaution; administered only if benefit outweighs risk.

8. Pneumococcal Vaccine (PCV/PPSV23)

9. Travel Vaccines (Situation-specific)

C. CONTRAINDICATED VACCINES IN PREGNANCY

D. POSTPARTUM VACCINATION (Catch-up)

• Tdap - if not given during pregnancy, give immediately postpartum
• MMR - if seronegative for rubella/measles; give postpartum
• Varicella - if seronegative; give postpartum
• Influenza - if non-immunized breastfeeding women
• All vaccines can be given while breastfeeding (safe), except yellow fever (precaution - avoid or temporarily suspend breastfeeding for 2 weeks)

Summary Table for Exam

Key Mnemonics for Exam

• T - Tdap (27-36 weeks)
• I - Influenza (any trimester, inactivated only)
• C - COVID-19 (any trimester)
• R - RSV (32-36 weeks)

• M - MMR
• V - Varicella
• V - Varivax (combined MMRV)
• H - (HPV - not recommended, delay)

Development of Placenta - Detailed Exam Answer

Introduction

1. Fetal part - derived from the chorionic sac (chorion frondosum)
2. Maternal part - derived from the endometrium (decidua basalis)

STEP 1: IMPLANTATION AND TROPHOBLAST DIFFERENTIATION (Days 6-9)

STEP 2: DECIDUAL REACTION (Week 2)

STEP 3: FORMATION OF CHORIONIC VILLI (Weeks 2-3)

Stage 1: Primary Chorionic Villi (End of Week 2)

• Cytotrophoblastic cells proliferate and invade the syncytiotrophoblast, forming finger-like projections - the primary chorionic villi.
• Structure: Core of cytotrophoblast covered by syncytiotrophoblast.
• At this stage, villi are solid cellular projections with no mesenchyme or blood vessels.

Stage 2: Secondary Chorionic Villi (Early Week 3)

• Extraembryonic mesoderm (from the extraembryonic coelom) invades the primary villi.
• This forms a central mesenchymal core inside each villus.
• Structure: Syncytiotrophoblast → Cytotrophoblast → Mesenchyme (centre)
• At this stage, villi cover the entire chorionic sac surface.

Stage 3: Tertiary Chorionic Villi (End of Week 3)

• Mesenchymal cells within the secondary villi differentiate into capillaries and blood cells (vasculogenesis).
• When blood vessels are visible within the villi = tertiary chorionic villi.
• The fetal capillary network connects with the embryonic heart via vessels in the connecting stalk.
• By end of Week 3, embryonic blood begins to flow through the villi.
• Gaseous exchange begins: O2 and nutrients diffuse from maternal blood in the lacunae → through villus walls → into fetal blood.

STEP 4: FORMATION OF THE INTERVILLOUS SPACE

• Maternal spiral arteries are eroded by the invasive syncytiotrophoblast.
• By Days 12-15, syncytiotrophoblast penetrates the endothelial lining of small spiral arteries - creating direct communication between lacunae and maternal blood vessels.
• The multiple lacunae merge into one large intercommunicating space = the intervillous space.
• Maternal blood (from ~120 spiral arteries) enters the intervillous space in pulsatile spurts and bathes the chorionic villi directly.
• The fetal villi project into this space "like a forest of trees" arising from the chorionic plate (analogous to soil).

STEP 5: DIFFERENTIATION INTO CHORION FRONDOSUM AND CHORION LAEVE (Week 8 onwards)

• Initially, chorionic villi cover the entire chorionic sac.
• As the chorionic sac grows:
  • Villi associated with decidua capsularis get compressed, lose their blood supply, and degenerate → forming the smooth, bare chorion laeve (smooth chorion)
  • Villi associated with decidua basalis become larger, branch profusely, and proliferate → forming the chorion frondosum (villous/bushy chorion)

STEP 6: MATURE PLACENTA STRUCTURE

Gross Anatomy (at term)

• Disc-shaped organ, ~15-20 cm diameter, ~2-3 cm thick, weighs ~500 g
• Fetal surface (chorionic plate): smooth, covered by amnion, umbilical cord attaches (usually centrally)
• Maternal surface (basal plate): rough, cotyledons visible (15-30 irregular lobes separated by decidual septa)

Cotyledons

• The maternal surface is divided into 15-30 cotyledons by decidual septa projecting from the decidua basalis.
• Each cotyledon contains 1-4 main stem villi (anchoring villi) and their branches.
• Each cotyledon is a functional vascular unit.

Types of Villi

STEP 7: THE PLACENTAL BARRIER (Hemochorial Placenta)

1. Syncytiotrophoblast (with brush border microvilli facing maternal blood)
2. Cytotrophoblast
3. Connective tissue / mesenchyme of villus
4. Fetal capillary endothelium

STEP 8: PLACENTAL CIRCULATION

Fetal Circulation

• Umbilical arteries (2) carry deoxygenated blood from fetus to placenta
• Blood passes through fetal capillaries in the chorionic villi
• Umbilical vein (1) carries oxygenated blood back to the fetus

Maternal Circulation

• ~120 spiral arteries open into the intervillous space
• Blood enters under arterial pressure, rises toward the chorionic plate, then percolates around the villi
• Drains back through endometrial veins
• Fetal and maternal circulations are SEPARATE - do not normally mix

STEP 9: PLACENTAL HOMEOBOX GENE REGULATION

• Homeobox genes (HLX, MSX2, DLX3) expressed in the trophoblast and its blood vessels induce trophoblastic invasion and regulate placental development - relevant for understanding abnormal placentation (placenta accreta, preeclampsia).

TIMELINE SUMMARY TABLE

CLINICAL CORRELATES (High-yield for exams)

Key Mnemonic

• Primary = cytotrophoblast core only (no mesenchyme)
• Secondary = Stroma (mesenchyme) invades
• Tertiary = Tubes (blood vessels/capillaries) appear inside