'TOTAL' (Tracheal Occlusion To Accelerate Lung Growth) Trial

Inclusion Criteria: 1. Patients aged 18 years or more, who are able to consent, 2. Singleton pregnancy, 3. Chromosomally normal fetus, 4. Gestation at randomization prior to 31 weeks plus 5 days or so that occlusion is done at the latest on 31 weeks plus 6 days, 5. Fetus is estimated to have moderate pulmonary hypoplasia, defined prenatally as: • O/E LHR 25-34.9% (included; irrespective of the position of the liver) • O/E LHR 35-44.9% (included) with intrathoracic liver herniation as determined by ultrasound or MRI. The O/E LHR will be determined by the FETO centers as follows: * Measurement of the contralateral lung area preferentially by the tracing method at the 4-chamber view of the heart; if by other method adjusted normative ranges must be used. * Measurement of the head circumference at the standard biparietal view of the head * The observed lung area: calculation of the LHR as the ratio of the measurements of the lung area to head circumference * The expected lung area is the lung area of a normal gestational age match, as determined by the head circumference of the index case in a normogram established for the same measurement method (tracing method in this case). A calculator for this will be available on the website of the study. * Calculation of the observed over expected lung area, 6. Acceptance of randomization and the consequences for the further management during pregnancy and thereafter, this includes the required observation following FETO surgery, which lasts up to 4 weeks after balloon is in place, 7. The patients must undertake the responsibility for either remaining close to, or at the FETO center, or being able to travel swiftly and within acceptable time interval to the FETO center until the balloon is removed. Intended postnatal treatment center must subscribe to suggested guidelines for "standardized postnatal treatment," and 8. Provide written consent to participate. 9. Fetus with no major anomalies that would impact the clinical course or outcomes. Exclusion Criteria: 1. Maternal contraindication to fetoscopic surgery or severe medical condition in pregnancy that make fetal intervention risky, 2. Technical limitations precluding fetoscopic surgery, such as severe maternal obesity, uterine fibroids or potentially others, not anticipated at the time of writing this protocol, 3. Preterm labor, cervix shortened (\<15 mm at randomization) or uterine anomaly strongly predisposing to preterm labor, placenta previa, 4. Patient age less than 18 years, 5. Psychosocial ineligibility, precluding consent, 6. Diaphragmatic hernia: right-sided or bilateral, major anomalies, isolated left-sided outside the O/E LHR limits for the inclusion criteria, and 7. Patient refusing randomization, to comply with required 4-week observation after balloon placement, or to comply with return to FETO center during the time period the airways are occluded or for elective removal of the balloon. 8. Patient allergic to latex.