Inclusion Criteria:
1. Pregnant women - maternal age 18 years or older and capable of consenting for their own participation in this study.
2. Singleton pregnancy.
3. MMC with the upper boundary located between T1 and S1.
4. Evidence of hindbrain herniation (confirmed on MRI to have an Arnold-Chiari type II malformation). An exception will be made for patients unable to have an MRI due to implants or any medical reasons. These patients will have the Arnold-Chiari type II malformation reviewed by ultrasonography.
5. Absence of chromosomal abnormalities and associated anomalies
6. Gestational age at the time of the procedure will be between 19 0/7 weeks and 25 6/7 weeks.
7. Normal karyotype and/or normal chromosomal microarray (CMA) by invasive testing (amniocentesis or Chorionic Villus Sampling (CVS)). If there is a balanced translocation with normal CMA with no other anomalies the candidate can be included. Patients declining invasive testing will be excluded. Results by flouorescence in situ hybridization (FISH) will be acceptable if the patient is at 24 weeks or more.
8. The family has considered and declined the option of termination of the pregnancy at less than 24 weeks.
9. The family meets psychosocial criteria (sufficient social support, ability to understand the requirements of the study).
10. Parental/guardian permission (informed consent) for follow up of the child after birth.
11. For totally percutaneous expandable port assisted cases: Appropriate anterior window on the uterus free of placental tissue, as assessed by ultrasound, such that direct access to the fetus through the maternal abdominal wall is possible. If this criteria is not met, patient may still be eligible for laparotomy assisted fetoscopic repair if all other inclusion criteria and no exclusion criteria are met.
Exclusion Criteria:
1. Fetal anomaly unrelated to MMC.
2. Severe kyphosis.
3. Increased risk for preterm labor including short cervical length (\<1.5 cm), history of incompetent cervix with or without cerclage, and previous preterm birth.
4. Placental abnormalities (previa, abruption, accreta) known at time of enrollment.
5. A pre-pregnancy body-mass index ≥40.
6. Contraindications to surgery including previous hysterotomy (whether from a previous classical cesarean, uterine anomaly such as an arcuate or bicornuate uterus, major myomectomy resection, or previous fetal surgery) in active uterine segment.
7. Technical limitations precluding fetoscopic surgery, such as uterine fibroids, fetal membrane separation, or uterine anomalies.
8. Maternal-fetal Rh alloimmunization, Kell sensitization or neonatal alloimmune thrombocytopenia affecting the current pregnancy.
9. Maternal HIV, Hepatitis-B, Hepatitis-C status positive because of the increased risk of transmission to the fetus during maternal-fetal surgery. If the patients HIV or Hepatitis status is unknown, the patient must be tested and found to have negative results before enrollment.
10. Maternal medical condition that is a contraindication to surgery or anesthesia.
11. Low amniotic fluid volume (Amniotic Fluid Index less than 6 cm) if deemed to be due to fetal anomaly, poor placental perfusion or function, or membrane rupture. Low amniotic fluid volume that responds to maternal hydration is not an exclusion criterion.
12. Patient does not have a support person (i.e. Spouse, partner, mother) available to support the patient for the duration of the pregnancy.
13. Inability to comply with the travel and follow-up requirements of the trial.
14. Participation in another intervention study that influences maternal and fetal morbidity and mortality or participation in this trial in a previous pregnancy.
15. Patient scores as severely depressed on the Edinburgh Postnatal Depression Scale
16. Maternal hypersensitivity to collagen.
17. Umbilical Cord hypercoiling or velamentous cord insertion
18. For totally percutaneous expandable port assisted cases: total anterior placentation
