Fetal Surgery and Prenatal Decision-Making

For many families, a diagnosis of myelomeningocele leads to a pivotal question: should we consider surgery before the baby is born? This choice involves a “shared decision-making” process between you and a multidisciplinary team of specialists ^[1].

The landmark Management of Myelomeningocele Study (MOMS) trial, and its follow-up study (MOMS2), provide the foundation for understanding the benefits and risks of fetal surgery ^[2][3]. It is important to understand that prenatal surgery is a specialized intervention to reduce the severity of the condition, but it is not a cure ^[4].

Am I a Candidate? (The Original MOMS Criteria)

Not every pregnancy is eligible for fetal surgery. The original MOMS trial established strict biological and practical criteria, though many specialized centers today use slightly expanded or individualized criteria. A formal evaluation at a fetal-therapy center is required to determine true eligibility ^[5]. Historical criteria included:

• Timing: Surgery typically between 19 weeks and 25 weeks, 6 days of pregnancy ^[6][7].
• Lesion Level: The opening in the spine located between the T1 and S1 vertebrae ^[8].
• Fetal Health: An “isolated” diagnosis with no other major unrelated structural or genetic abnormalities, and evidence of hindbrain herniation (Chiari II) ^[8].
• Maternal Health: Factors such as a BMI under 35, no prior history of preterm birth, and a healthy uterus without major fibroids or placental issues ^[8][5].
• Social Support: Centers evaluated whether the family had the support system needed for travel and potential bed rest, which is a practical requirement, not a biological one ^[1][9].

The Potential Benefits for the Baby

The primary goal of fetal surgery is to protect the spinal cord from further damage while it is still developing. Research has shown population-level advantages for children who undergo prenatal repair compared to postnatal repair, though outcomes vary for each child:

1. Reduced Hydrocephalus: In the original MOMS trial, approximately 40% of the prenatal surgery group required a shunt (a tube to drain fluid from the brain) by age one, compared to 82% of the postnatal group ^[2].
2. Improved Mobility: At 30 months old, children in the prenatal group were more likely to walk independently (44.8% vs. 23.9%) ^[6].
3. Bladder Function: Bladder outcomes are less definitive. While some evidence suggests fewer children in the prenatal group require clean intermittent catheterization at 30 months, urinary issues often persist. Families should not expect normal bladder or bowel function after fetal repair ^[10].

The Risks to the Mother and Pregnancy

The benefits to the baby must be weighed against significant risks to the mother and the current and future pregnancies. Open fetal surgery involves a large incision in the mother’s uterus (hysterotomy), which is more invasive than a standard C-section ^[11].

• Preterm Birth: Fetal surgery increases the risk of Preterm Premature Rupture of Membranes (PPROM)—where the water breaks too early—and spontaneous labor ^[12]. In the MOMS trial, the average delivery age for prenatal surgery was 34 weeks ^[2].
• Uterine Scarring and Dehiscence: The incision in the uterus can thin or separate (dehiscence) as the pregnancy progresses. In the MOMS trial, this occurred in 34% of cases ^[13].
• Future Pregnancies: Once you have open fetal surgery, all future deliveries must be by C-section to prevent the scar from tearing. There is a small but serious risk of complete uterine rupture (about 9% in subsequent pregnancies) and severe placental complications (like placenta previa or accreta) ^[14][15].

Open vs. Fetoscopic Surgery

Some centers now offer fetoscopic repair, which uses small ports and cameras (similar to “keyhole” surgery) instead of a large uterine incision. This is an evolving, specialized option.

• Fetoscopic Benefits: Because it requires smaller incisions, it may allow for a vaginal delivery and reduce the long-term uterine scarring that affects future pregnancies ^[13][15]. However, vaginal delivery is never guaranteed.
• Fetoscopic Risks: Currently, fetoscopic surgery has a very high rate of PPROM (up to 80%, compared to roughly 31-46% for open surgery depending on the cohort), and a higher risk of the baby being born very early ^[15]. Long-term outcomes for the baby are also less established than the open-surgery MOMS evidence.

Making the Decision

There is no “right” choice—only the choice that is right for your family. Postnatal repair (waiting until after birth) is a safe, standard-of-care option that avoids all maternal surgical risks and allows the baby to be born closer to their due date ^[2]. Prenatal surgery offers a chance for better motor function and less brain fluid buildup but carries the weight of maternal and obstetric risks. Because the window for fetal surgery is time-limited, prompt referral to a maternal-fetal medicine center is essential ^[1].