Fetal Pericardial Effusion

Fetal pericardial effusion is fluid around the fetal heart, found on ultrasound as an anechoic rim in the pericardial sac. A small rim of 2 mm or less is a normal finding in many fetuses, and larger effusions (above 2 mm) are abnormal. Causes include heart failure, hydrops, infection, anaemia, chromosomal abnormality, cardiac tumours and diverticulum. It matters because it may signal cardiac or systemic disease that needs a full work up.

• Isolated small effusions rarely cause harm.
• Risk factors: parvovirus and cytomegalovirus infection, fetal anaemia, heart block, structural heart disease.
• Tamponade is rare in the fetus.

Women are usually unaware, and the finding is made on a routine scan. Hydrops may cause a large uterus and reduced movements.

• No symptoms in the mother.
• Other effusions may be present.
• Differential diagnosis: normal physiological fluid, pleural effusion, thymus appearance, cardiac tumour, hydrops fetalis, cardiomyopathy, heart failure from arrhythmia.
• Complications: hydrops fetalis, cardiac compromise, tamponade, stillbirth, neonatal cardiac failure.

The approach is to measure the effusion and look for the cause.

• Ultrasound: depth of fluid (above 2 mm, or above 2 mm at both sides of the heart), whether the effusion is isolated or accompanied by ascites, pleural fluid or skin oedema.
• Fetal echocardiography for structural disease, ventricular function, valve regurgitation, tumours and rhythm.
• Maternal tests: TORCH serology, parvovirus B19 IgM, syphilis, HIV, blood group and antibody screen; middle cerebral artery peak systolic velocity for anaemia.
• Amniocentesis for karyotype and microarray when other anomalies are present.

The principle is observation of small isolated effusions and treatment of the cause for larger or progressive ones.

• Supportive: scan every 1 to 2 weeks until stable; daily fetal movement counts; deliver in a unit with neonatal cardiology.
• Pharmacological: tachyarrhythmia: digoxin 0.5 mg oral 8-hourly for 3 doses then 0.25 mg oral 12-hourly; syphilis: benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks; anaemia: intrauterine transfusion; cytomegalovirus infection: valaciclovir 2 g oral 6-hourly; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if preterm delivery is likely.
• Procedures: fetal pericardiocentesis by a fetal medicine specialist for large effusions with cardiac compromise; delivery at term, earlier for progressive hydrops or worsening heart function, with a neonatal team ready.
• Red flags: increasing effusion, hydrops, falling fetal heart rate, reduced fetal movements, ventricular dysfunction.
• Follow-up: scan every 1 to 2 weeks; echocardiography after 2 weeks; newborn echocardiography within 24 hours of birth.