Balloon in the womb: new hope for babies with rare birth defect?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Pregnant person age 18 years or older * Singleton pregnancy * Normal fetal karyotype with confirmation by culture results, Chromosomal Microarray (CMA) with non-pathological variants, Whole Exome Sequencing (WES) or Whole Genome Sequencing (WGS). Results by florescence in situ hybridization (FISH) will be acceptable if the patient is \>26 weeks gestation * Gestational age at enrollment less than 29 weeks 6 days * Intrathoracic liver herniation * Isolated left Congenital Diaphragmatic Hernia (CDH) with Lung to Head Circumference Ratio (LHR) \<30% at enrollment OR isolated right CDH with LHR \<= 45% at enrollment * Cervical length by transvaginal ultrasound \>= 20 mm within 24 hours of FETO procedure * Psychosocial criteria * Able to provide informed consent Exclusion Criteria: * Patient \< 18 years of age * Multi-fetal pregnancy * History of natural rubber latex allergy * Preterm labor, cervix shortened (\<20 mm at enrollment or within 24 hours of FETO balloon insertion procedure) or uterine anomaly strongly predisposing to preterm labor or placenta previa * Psychosocial ineligibility precluding consent * Inability to reside within 30 minutes of OHSU * Inability to comply with the travel for the follow-up requirements of the trial * Lack of a support person (e.g., spouse, partner, mother) available to stay with the patient for the duration of the pregnancy at OHSU. * Bilateral CDH, isolated left sided CDL with LHR \>= 30% or isolated right side CDH with LHR \>45% as determined by ultrasound * No intrathoracic liver herniation * Additional fetal anomaly and chromosomal abnormalities, associated anomalies recognized to alter survival prognosis (i.e. congenital heart disease) or presence of an underlying genetic syndrome (i.e. Fryns) by ultrasound, MRI, or echocardiogram at the fetal treatment center * Maternal contraindication to fetoscopic surgery or severe maternal medical condition in pregnancy * History of incompetent cervix with or without cerclage * Placental abnormalities (previa, abruption, accreta) known at time of enrollment * Maternal-fetal Rh isoimmunization, Kell sensitization or neonatal alloimmune thrombocytopenia affecting the current pregnancy * Maternal HIV, Hepatitis-B, Hepatitis-C status positive because of the increased risk of transmission to the fetus during maternal-fetal surgery. If the patient's HIV or Hepatitis status is unknown, the patient must be tested and found to have negative results before enrollment * Uterine anomaly such as large or multiple fibroids or Mullerian duct abnormality * No safe or technically feasible fetoscopic approach to balloon placement * Participation in another intervention study that influences maternal and fetal morbidity and mortality or participation in this trial in a previous pregnancy.