What are the causes of edema in a 30-week pregnant woman?

Causes of Edema at 30 Weeks of Pregnancy

Edema at 30 weeks of pregnancy is predominantly physiological, caused by the 40-50% increase in blood volume, venous obstruction from the enlarged uterus, and altered Starling forces that shift fluid into the interstitial space—this affects up to 60% of normal pregnancies and requires no treatment unless accompanied by hypertension or proteinuria. 1, 2

Physiological (Normal) Causes

Hemodynamic Changes

• Plasma volume expansion reaches maximum of 40% above baseline by 24 weeks gestation, creating foundational conditions for edema development 1, 2
• Cardiac output increases by 30-50% during normal pregnancy, with stroke volume rising in early pregnancy and heart rate becoming the major factor in late pregnancy 1
• Systemic vascular resistance decreases through active vasodilation mediated by prostacyclin and nitric oxide, with diastolic blood pressure falling approximately 10 mmHg below baseline in the second trimester 1, 2

Mechanical Factors

• Inferior vena caval compression by the gravid uterus causes venous stasis and obstruction to venous return, particularly affecting the lower extremities 1, 2
• Increased hydrostatic pressure in lower extremity veins results from mechanical obstruction, worsening with prolonged standing or sitting 2, 3
• Starling forces shift unfavorably, with narrowing of the oncotic-wedge pressure gradient that increases susceptibility to interstitial fluid accumulation 2, 3

Biochemical Changes

• Total body water increases with at least 25% distributed to the interstitial space, ultimately manifesting as lower leg edema 3
• Cumulative sodium retention occurs throughout pregnancy, contributing to fluid retention 3
• Changes in extracellular matrix hydration add to the fluid shift into interstitial spaces 3

Pathological Causes Requiring Urgent Evaluation

Pre-eclampsia (Most Critical)

• New-onset hypertension (BP ≥140/90 mmHg) developing after 20 weeks gestation with proteinuria (≥0.3 g/24 hours) or evidence of maternal organ dysfunction 1, 4
• Severe pre-eclampsia presents with BP ≥160/100 mmHg, requiring immediate hospitalization 1, 2
• Third trimester timing is particularly high-risk, as increases in estrogens and placental prolactogenic hormones are associated with worsening symptoms 1
• Edema with low serum protein levels (51-56 g/L) combined with even mild hypertension can signal imminent development of HELLP syndrome 5

HELLP Syndrome

• Hemolysis, Elevated Liver enzymes, Low Platelets represents the severe end of the pre-eclampsia spectrum 4
• Epigastric or right upper quadrant pain with edema after 20 weeks gestation requires immediate laboratory evaluation including complete blood count, liver enzymes, serum creatinine, and urinalysis 4
• Elevated lactate dehydrogenase indicates both hepatocellular damage and hemolysis 4

Cardiac Causes

• Peripartum cardiomyopathy is the most common cause of severe cardiovascular complications in pregnancy 1
• Pre-existing cardiac disease can decompensate due to the 30-50% increase in cardiac output 1
• Pulmonary edema in hypertensive women, particularly with pre-eclampsia, requires immediate management with oxygenation, ventilation, and venodilators 6

Thromboembolic Disease

• Deep venous thrombosis must be considered with unilateral, severe, or painful swelling, especially in the left leg 2
• Hypercoagulable state develops due to increased coagulation factors, fibrinogen, platelet adhesiveness, and diminished fibrinolysis 1, 2
• Venous stasis from uterine obstruction further increases thromboembolic risk 1

Rare Causes

• Hereditary angioedema (HAE-C1-INH) can worsen in the third trimester due to increased estrogens and placental prolactogenic hormones, with abdominal attacks occurring more frequently during pregnancy 1

Clinical Approach and Red Flags

When Edema is Physiological

• Bilateral lower extremity edema that worsens with prolonged standing and improves with leg elevation 2, 3
• No hypertension (BP <140/90 mmHg) and no proteinuria 1, 2
• Normal serum protein levels (>60 g/L) 5

When Immediate Evaluation is Mandatory

• Any hypertension (BP ≥140/90 mmHg) with edema requires evaluation for pre-eclampsia 1, 2, 4
• Proteinuria (≥0.3 g/24 hours or dipstick 2+ or more) with edema 1, 4
• Unilateral or asymmetric edema, particularly if painful, requires evaluation for deep venous thrombosis 2
• Edema with low serum protein levels (<60 g/L) and any degree of hypertension signals potential HELLP syndrome development 5
• Epigastric or right upper quadrant pain with edema after 20 weeks requires immediate laboratory workup 4
• Dyspnea or orthopnea with edema suggests cardiac decompensation or pulmonary edema 6

Management of Physiological Edema

• Graduated compression stockings are recommended for all pregnant women with lower limb edema 2, 7
• Leg elevation during rest periods helps reduce edema accumulation 2, 8
• Early mobilization and adequate hydration should be maintained throughout pregnancy 2
• Appropriate physical exercise combined with compression therapy effectively prevents and treats lower limb edema 2, 7, 8
• Avoid supine positioning in late pregnancy to prevent inferior vena caval compression 1, 2
• Diuretics should be restricted to pulmonary edema of pre-eclampsia and are not indicated for management of physiological pregnancy edema 3