Inclusion Criteria:  Women carrying a fetus with isolated CDH eligible for FETO, i.e. with severe or moderate hypoplasia:  Left sided CDH with severe (i.e. quotient of observed-to-expected- lung-to-head ratio under 25%) or moderate pulmonary hypoplasia (observed-to-expected- lung-to-head ratios of 25 to 34.9% (any liver position), or 35 to 44.9% with intrathoracic liver herniation) Right sided CDH with severe pulmonary hypoplasia (quotient of observed-to-expected- lung-to-head ratio under 50%) Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures Maternal age of 18 years or older Single pregnancy Signed informed consent Consent to have an ultrasound of the uterus after delivery when indicated Postnatal management center agrees to participate  Exclusion Criteria:  Participants eligible for this Trial must not meet any of the following criteria:  History of allergy to latex Contraindication to fetoscopy and FETO (maternal diseases or technical limitations making prenatal surgery hazardous or impossible) Premature Membrane Rupture (PROM) Multiple pregnancy Maternal age less than 18 years Refusal to stay close to the UZ Leuven until balloon removal Any disorder, which in the Investigator's opinion might jeopardise the participant's safety or compliance with the protocol Any prior or concomitant treatment(s) that might jeopardise the participant's safety or that would compromise the integrity of the Trial Participation in another interventional trial with an investigational medicinal product (IMP) or device