Fetal Pleural Effusion

Fetal pleural effusion is the collection of fluid in the fetal pleural space, found on ultrasound as an anechoic area around the lung. It may be primary (chylothorax from lymphatic leak) or secondary to hydrops, infection, anaemia, heart disease, chromosomal abnormality or lung masses. Large effusions compress the lung and cause pulmonary hypoplasia and death.

• Isolated unilateral effusions have a better outlook than bilateral or those with hydrops.
• Risk factors: male fetus, Down syndrome, Turner syndrome, Noonan syndrome, infection.
• Small effusions may resolve without treatment.

Women are usually asymptomatic, though polyhydramnios and a large uterus may be present. Reduced fetal movements and a falling fetal heart rate are late signs.

• Fundal height large for dates from polyhydramnios.
• Often found at the anomaly scan.
• Differential diagnosis: congenital diaphragmatic hernia, congenital pulmonary airway malformation, pulmonary sequestration, cardiac failure with hydrops, pericardial effusion, chylothorax, infection.
• Complications: pulmonary hypoplasia, hydrops fetalis, polyhydramnios, preterm labour, stillbirth, neonatal respiratory failure, neonatal death.

The approach is a detailed scan to define the side, size and effect on the mediastinum, with tests for the cause.

• Ultrasound: unilateral or bilateral fluid, lung compression (lung to head ratio), mediastinal shift, flattened diaphragm, polyhydramnios, ascites, skin oedema.
• Fetal echocardiography; middle cerebral artery peak systolic velocity for anaemia.
• Maternal tests: blood group and antibody screen, TORCH serology, parvovirus B19, syphilis, HIV, glucose.
• Fetal thoracocentesis: fluid cell count (lymphocytes above 80 percent confirms chylothorax); amniocentesis for karyotype and microarray.

The principle is observation of small stable effusions and drainage by shunt for large or progressive effusions.

• Supportive: refer to a fetal medicine unit; scan every 1 to 2 weeks; daily fetal movement counts; deliver in a unit with neonatal intensive care and chest drainage skills.
• Pharmacological: betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery is likely; parvovirus or alloimmune anaemia: intrauterine transfusion; syphilis: benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks; tachyarrhythmia: digoxin 0.5 mg oral 8-hourly for 3 doses then 0.25 mg oral 12-hourly; neonatal chylothorax: octreotide 1 microgram/kg/hour IV infusion, increased by 1 microgram/kg/hour daily to a maximum of 10 micrograms/kg/hour, with feeds of medium chain triglyceride formula.
• Procedures: thoracoamniotic shunt for effusions that cause mediastinal shift, polyhydramnios or hydrops; single thoracocentesis to confirm the cause and test lung re-expansion; delivery at 37 to 38 weeks, with controlled neonatal drainage, intubation and chest drain.
• Special groups: effusion with hydrops from chromosomal abnormality has a poor prognosis and needs genetic counselling before intervention.
• Red flags: mediastinal shift, hydrops, polyhydramnios, falling fetal heart rate, reduced fetal movements, preterm contractions.
• Follow-up: scan every 1 to 2 weeks; check shunt position weekly; newborn chest X-ray and respiratory support; infant feeding and growth review.