Hydrops: Definition, Diagnosis, and Management

What is Hydrops?

Hydrops fetalis is a serious fetal condition defined as abnormal accumulation of fluid in two or more extravascular fetal compartments, including ascites, pleural effusion, pericardial effusion, and skin edema (>5 mm). 1, 2 The condition represents a final common pathway for numerous underlying pathologies and results from an imbalance in fluid regulation between the vascular and interstitial spaces. 3

Classification

Non-immune hydrops fetalis (NIHF) accounts for >90% of all hydrops cases in the Western world, occurring without evidence of blood group isoimmunization. 1, 2, 3
Immune hydrops results from maternal antibodies against fetal red blood cells (historically Rh disease). 4

Diagnostic Workup

Initial Evaluation

Begin with an indirect Coombs test to confirm non-immune etiology, followed immediately by detailed fetal ultrasound with comprehensive echocardiography and middle cerebral artery (MCA) Doppler. 5, 6 These three studies constitute the core diagnostic algorithm. 5

Ultrasound Assessment Must Include:

All fluid-filled compartments (ascites, pleural/pericardial effusions, skin edema >5 mm) 5
Structural anomalies throughout the fetal anatomy 1
Placental thickness (placentomegaly may be present) 7
Comprehensive fetal echocardiography to identify structural cardiac defects and arrhythmias 1, 5

MCA Doppler: The Critical Decision Point

Peak systolic velocity >1.5 multiples of the median (MoM) indicates fetal anemia requiring urgent intervention. 1, 5
This measurement determines whether immediate intrauterine transfusion is needed. 5

Genetic and Infectious Testing

Obtain fetal karyotype and/or chromosomal microarray analysis regardless of whether structural anomalies are identified. 1, 5 This is non-negotiable because:

Chromosomal abnormalities account for 7-16% of NIHF cases 1
Aneuploidy confers extremely poor prognosis with very high intrauterine fetal death rates 5, 8
Turner syndrome (45,X) and trisomy 21 are the most common chromosomal causes 1

Additional Testing Based on Findings:

Parental mean corpuscular volume (MCV) screening: If either parent has MCV <80 fL, perform DNA testing for alpha-thalassemia (accounts for 10-55% of NIHF in Southeast Asian populations) 1, 5
Amniocentesis for infectious workup: PCR testing for cytomegalovirus, parvovirus B19, and toxoplasmosis when infection is suspected 1, 5
Amniotic fluid alpha-fetoprotein to evaluate for congenital nephrosis or other protein-losing conditions 1

Etiology and Pathophysiology

Most Common Causes (in order of frequency):

Cardiovascular abnormalities (17-35%): Structural heart defects, arrhythmias, cardiomyopathy 1, 8
- Right heart defects are most common 1
- Combined fetal-infant mortality is 92% for cardiac structural abnormalities 1, 8
Chromosomal abnormalities (7-16%): Turner syndrome, trisomy 21, trisomies 13/18 1, 8
Hematologic disorders (4-12%): Alpha-thalassemia, fetal anemia from various causes 1
Infectious causes (5-7%): Parvovirus B19 (most common), CMV, toxoplasmosis 1, 4
Thoracic abnormalities (6%): Congenital pulmonary airway malformation (CPAM), pleural effusions, chylothorax 1
Twin-twin transfusion syndrome (3-10%): Hypervolemia in recipient twin 1
Idiopathic (15-25%): No cause identified despite thorough evaluation 1

Pathophysiologic Mechanisms:

Increased central venous pressure (cardiac defects, thoracic masses) 1
High-output cardiac failure (severe anemia, large tumors) 1
Hypoproteinemia (congenital nephrosis, protein-losing enteropathy) 1
Lymphatic obstruction or dysplasia (Turner syndrome, chylothorax) 1
Increased capillary permeability (infection, endothelial damage) 1

Management by Etiology

Fetal Arrhythmias

Administer transplacental antiarrhythmic medications for supraventricular tachycardia, atrial flutter, or atrial fibrillation unless gestational age is near term or maternal contraindications exist. 1, 5 This is first-line therapy with good outcomes. 5

Third-degree atrioventricular block with hydrops has extremely poor prognosis: Corticosteroid therapy offers no benefit, and in-utero treatment remains investigational. 1, 5

Fetal Anemia

Perform intrauterine transfusion when MCA-PSV >1.5 MoM confirms anemia secondary to parvovirus B19 infection or fetomaternal hemorrhage, unless pregnancy is at advanced gestational age where delivery risks are lower than procedural risks. 1, 5

Parvovirus B19 causes transient red cell aplasia; transfusion can support the fetus through the aplastic crisis 1
Risk of fetal death is 15% at 13-20 weeks and 6% after 20 weeks 1
Outcomes are significantly improved with intrauterine transfusion 1

Thoracic Abnormalities

Drain large unilateral pleural effusions via needle drainage or thoracoamniotic shunt placement for hydrothorax, chylothorax, or effusions associated with bronchopulmonary sequestration. 1, 5

Chylothorax diagnosis confirmed by >80% lymphocytes in pleural fluid 1
Reported survival exceeds 50% in hydropic fetuses treated with thoracoamniotic shunt 1
For macrocystic CPAM, needle drainage is effective 1
For microcystic CPAM, corticosteroid therapy is first-line treatment 1

Twin-Twin Transfusion Syndrome

Laser therapy is the best available approach for severe cases with hydrops 1
Selective termination via umbilical cord coagulation is an alternative option 1

Obstetric Management Principles

Delivery Timing

Avoid preterm delivery before 34 weeks as prematurity significantly worsens the already poor prognosis. 5, 6 However:

At 34 weeks gestation with worsening hydrops, proceed with delivery as risks of continued pregnancy outweigh potential benefits 5
For stable cases without maternal complications, continue expectant management with planned delivery at 37-38 weeks 5, 6

Antenatal Corticosteroids

Administer corticosteroids for pregnancies with non-lethal or potentially treatable etiologies that may require preterm delivery. 5 While specific survival benefit for hydrops is limited (two retrospective series showed no improvement), standard prematurity benefits still apply. 5

Antepartum Surveillance

Initiate fetal surveillance only when three criteria are met: 5, 6

Underlying etiology is not lethal
Pregnancy has reached viable gestational age
Surveillance findings will guide delivery timing

Mode of Delivery

Perform cesarean delivery if the fetus is potentially treatable or viable and delivery is based on antepartum surveillance findings or concern about fetal deterioration. 5, 6

Assess for large pleural or pericardial effusions before birth; drainage may be required pre-delivery to improve neonatal resuscitation 5
Evaluate risk of dystocia from severe anasarca or massive effusions 5

Delivery Location

All pregnancies with potentially treatable or idiopathic NIHF must deliver at a tertiary center with Level III NICU capability to stabilize and treat critically ill neonates. 5, 8, 6 Transfer the mother before delivery if not already at such a facility. 5

Maternal Monitoring

Monitor maternal blood pressure serially throughout pregnancy to detect mirror syndrome. 1, 5, 6 Mirror syndrome is a form of severe preeclampsia characterized by maternal edema "mirroring" fetal hydrops, and it necessitates delivery in most cases. 1, 5, 6

Prognosis and Counseling

Overall neonatal survival is often <50% even in the absence of aneuploidy, and aneuploidy confers extremely poor prognosis. 5, 8, 6

Prognosis by Etiology:

Cardiac structural abnormalities: 92% combined fetal-infant mortality 1, 8
Treatable arrhythmias and parvovirus B19: Comparatively better outcomes with intervention 5, 8
Isolated chylothorax: Mortality as low as 6%, but up to two-thirds when associated with other anomalies 8
Chromosomal abnormalities: Extremely poor prognosis with very high intrauterine death rates 5, 8

Additional Prognostic Factors:

Younger gestational age at diagnosis predicts higher mortality 8
Low 5-minute Apgar score and need for high-level respiratory support on day 1 predict poor outcomes 8
Preterm birth <34 weeks is a significant poor prognostic factor 5

Long-term Outcomes in Survivors:

Parvovirus B19 survivors may have delayed psychomotor development and abnormal neurological outcomes 8
Fetuses with supraventricular tachycardia may develop Wolff-Parkinson-White syndrome later in life 8

Critical Pitfalls to Avoid

Do not delay genetic testing even when structural anomalies are absent—aneuploidy must be ruled out 1, 5
Do not deliver at a facility lacking Level III NICU—this significantly worsens prognosis 5, 6
Do not pursue expectant management at 34 weeks with worsening hydrops—delivery is indicated 5
Do not assume vaginal delivery is safe without evaluating for large effusions that could compromise resuscitation 5
Do not miss mirror syndrome—serial maternal blood pressure monitoring is essential 1, 5, 6
Do not withhold intrauterine transfusion for parvovirus-related anemia unless near term—outcomes are significantly improved with intervention 1, 5

What is hydrops and how is it diagnosed and managed in its various forms (fetal hydrops, corneal hydrops, serous otitis media, peripheral lymphedema)?

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