Left diaphragmatic hernia detected during fetal life carries a high risk for postnatal lung failure due to lung underdevelopment and pulmonary hypertension. In severe cases, extracorporeal membrane oxygenation (ECMO) is used as a life-saving intensive care means to enable survival of severely affected infants.

Clinical experience from prospective controlled non-randomized case series with fetoscopic tracheal balloon occlusion has seen improved survival rates in contrast to untreated controls.

Therefore, the purpose of this randomized clinical trial in a less severely affected subgroup of patients is whether by fetoscopic tracheal occlusion, the intensity of postnatal intensive care therapy might be reduced. Primary outcome measure is the need for postnatal ECMO therapy.

Inclusion Criteria:

• Pregnant women from European countries carrying fetuses with left diaphragmatic hernia.
• Normal karyotype, no further severe anomalies on prenatal ultrasound study.
• Fetal liver herniation into the chest; gestational age-related lung volume between 20-25% of normal as determined by magnetic resonance imaging between 30+0 - 34+0 weeks+days of gestation.

Exclusion Criteria:

• Any maternal disease or condition that would result in an increased risk to her health from the experimental procedure.
• Abnormal fetal karyotype, further severe fetal anomalies on prenatal ultrasound.