Pregnancy is often called a state of “physiological stress” because almost every system of a woman’s body undergoes dramatic changes to support the developing fetus. These adaptations are normal, expected, and essential for a healthy pregnancy. However, they also explain why women experience symptoms like fatigue, nausea, edema, back pain, or anemia during gestation.
For healthcare students and professionals, understanding pregnancy physiology is vital to differentiate between normal adaptations and pathological conditions.
This article provides a system-by-system breakdown of pregnancy physiology, with clinical relevance for obstetrics, nursing, and medicine.
Hormonal Changes in Pregnancy
Hormones play a central role in regulating maternal physiology and ensuring successful fetal development.
Prolactin – Produced by the anterior pituitary; stimulates breast development and prepares mammary glands for lactation.Clinical Significance:
- Estrogen and progesterone imbalance can affect pregnancy viability.
- hCG is the basis for pregnancy tests.
- Relaxin increases joint mobility but may predispose to back and pelvic pain.
Cardiovascular Changes
↑ Cardiac output: due to ↑ stroke volume and ↑ heart rate (10–15 bpm increase).Clinical Relevance:
- Increased cardiac workload may unmask latent heart disease.
- Supine hypotension syndrome may occur due to vena cava compression by the gravid uterus.
Respiratory Changes
↑ Basal metabolic rate (BMR) and oxygen demand.Clinical Relevance:
- Pregnant women may feel breathless (dyspnea of pregnancy), which is normal unless associated with other symptoms.
Renal and Urinary Changes
↑ Glomerular Filtration Rate (GFR) due to increased plasma volume.Clinical Relevance:
- Must distinguish between normal urinary frequency and UTI.
- Edema may be physiological, but sudden swelling can signal preeclampsia.
Gastrointestinal Changes
Heartburn (Pyrosis): Progesterone relaxes the lower esophageal sphincter.Clinical Relevance:
- Persistent vomiting may indicate hyperemesis gravidarum.
- Hemorrhoids often resolve postpartum but may cause severe discomfort.
Musculoskeletal Changes
- Lordosis: Center of gravity shifts forward, causing inward spinal curvature.
- Low back pain common.
- Carpal tunnel syndrome due to fluid retention.
- Calf cramps frequent.
Clinical Relevance:
Proper posture and physiotherapy can relieve musculoskeletal discomfort.Endocrine (Thyroid and Pituitary) Changes
Thyroid:
- ↑ Thyroxine → higher metabolism and appetite.
- Some women may develop a goiter (thyroid enlargement).
Pituitary:
- ↓ FSH and LH due to high progesterone.
- ↑ Prolactin (for lactation).
- ↑ Oxytocin near delivery.
Clinical Relevance:
- Thyroid dysfunction (hypo/hyperthyroidism) can complicate pregnancy outcomes.
Skin Changes
- Striae gravidarum (stretch marks) – due to collagen stretching.
- Chloasma (mask of pregnancy): hyperpigmentation of cheeks, nose, and forehead.
- Linea nigra: dark vertical line on abdomen.
- Montgomery glands: hypertrophy of sebaceous glands on areola.
Clinical Relevance:
- Most skin changes are cosmetic and fade postpartum.
Hematological Changes
- ↑ Plasma volume more than RBC mass → hemodilution → physiological anemia of pregnancy.
- ↑ Fibrinogen: Pregnancy is a hypercoagulable state → ↑ risk of DVT (deep vein thrombosis).
- ↑ WBCs, ↓ Platelets.
Clinical Relevance:
- Anemia requires monitoring; pathological anemia must be differentiated.
- Hypercoagulability increases the need for early ambulation postpartum.
Summary Table: Physiological Changes During Pregnancy
| System | Major Change | Clinical Effect |
|---|---|---|
| Hormones | ↑ Estrogen, Progesterone, hCG, Prolactin, Oxytocin | Supports fetal growth, lactation, prevents menstruation |
| Cardiovascular | ↑ Cardiac output, mild heart enlargement | Physiological murmurs, risk in heart disease |
| Respiratory | ↑ BMR, mild alkalosis | Breathlessness (normal) |
| Renal | ↑ GFR, urinary stasis | Frequency, edema, ↑ risk of UTI |
| GI | ↓ Motility, relaxed LES | Heartburn, constipation, hemorrhoids |
| Musculoskeletal | Lordosis, joint relaxation | Back pain, carpal tunnel |
| Thyroid | ↑ Thyroxine, possible goiter | ↑ Metabolism, appetite |
| Pituitary | ↑ Prolactin, ↑ Oxytocin | Lactation, labor onset |
| Skin | Striae, chloasma, linea nigra | Cosmetic, temporary |
| Hematology | Hypercoagulable, dilutional anemia | Risk of DVT, mild anemia |
FAQs on Pregnancy Physiology
Q1. Why do pregnant women develop physiological anemia?
Because plasma volume increases more than RBC volume, causing hemodilution.
Q2. Why is pregnancy considered a hypercoagulable state?
Due to ↑ fibrinogen, which helps prevent hemorrhage at delivery but increases risk of DVT.
Q3. Why do women get heartburn during pregnancy?
Progesterone relaxes the lower esophageal sphincter, allowing gastric reflux.
Q4. What is the significance of linea nigra and chloasma?
They are pigmentary changes due to hormonal stimulation, considered benign and temporary.
Q5. Why does urinary frequency occur in pregnancy?
Because of increased GFR, plasma volume, and uterine pressure on the bladder.
