Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 22 peer-reviewed journal articles Updated
Neurosurgery · Spina Bifida

Understanding Spina Bifida: Types and Biology

At a Glance

Spina bifida is a neural tube defect where the spine does not close properly in early pregnancy. It is categorized into open defects like myelomeningocele and closed defects like spina bifida occulta. Causes involve a mix of genetics and environmental factors, including low folic acid levels.

Receiving a diagnosis of spina bifida for your child can feel overwhelming and evoke a wide range of emotions, from fear and confusion to deep concern for the future. It is important to know that you are not alone, and understanding the biological foundations of this condition is a powerful first step in navigating the path ahead. Spina bifida is a type of neural tube defect (NTD)—a condition where the brain, spinal cord, or their protective coverings do not develop fully during the first few weeks of pregnancy [1][2].

The Biology of Development

To understand spina bifida, it helps to look at how the spine forms. In early pregnancy, a flat layer of cells called the neural plate normally folds inward to form a tube [3]. This process, called neurulation, usually happens within the first 28 days after conception—often before a person even knows they are pregnant [1].

  • Primary Neurulation: The top part of the tube folds and fuses together. If this fails, it results in “open” defects [2][3].
  • Secondary Neurulation: The lower part of the spine forms from a solid mass of cells that later hollows out. If this process is disrupted, it typically leads to “closed” defects [3][4].

Types of Spina Bifida

Doctors generally categorize spina bifida into two main groups based on whether the defect is covered by skin.

Open Spinal Dysraphism (Spina Bifida Aperta)

In these cases, the spinal canal is open to the environment, and there is no skin covering the defect [5].

  • Myelomeningocele: This is the most common and severe form of open spina bifida [6]. A sac containing part of the spinal cord and nerves pushes through an opening in the back. Because the nerves are exposed to amniotic fluid during pregnancy, they can become damaged, often leading to challenges with walking and bladder or bowel control [7][8].
  • Meningocele: In this rarer form, a sac of fluid pushes through the opening, but the spinal cord itself is not inside the sac [6]. Because the nerves are often intact, the neurological effects are usually less severe than in myelomeningocele [7].

Closed Spinal Dysraphism (Spina Bifida Occulta)

These defects are covered by skin and are often discovered later in life or through specialized imaging [5].

  • Spina Bifida Occulta: Often called “hidden” spina bifida, this is a small gap in the bones of the spine. It is very common and frequently causes no symptoms or disabilities [5]. Sometimes, a small tuft of hair, a dimple, or a birthmark on the back may be the only outward sign.
  • Lipomyelomeningocele: A form of closed dysraphism where fatty tissue attaches to the spinal cord [9]. This can sometimes cause the cord to become “tethered” or pulled, which may require monitoring or surgery as the child grows [4][10].

Why Does This Happen?

Spina bifida is polygenic, meaning it is caused by a complex mix of many different genetic and environmental factors rather than a single cause [11][12].

The Role of Folic Acid

One of the most well-known environmental factors is folic acid (Vitamin B9). Folic acid is essential for the cells to divide and fold properly during the creation of the neural tube [13]. Research has shown that taking folic acid supplements ideally 1 to 3 months before conception and during early pregnancy significantly reduces the risk of neural tube defects [1][14]. While it is a vital preventive tool, it is important to understand that some cases of spina bifida occur even when folic acid intake is sufficient [13].

Other Risk Factors

Other factors that can increase the risk include:

  • Maternal Health: Conditions like pregestational diabetes or obesity [15][16].
  • Medications: Certain anti-seizure medications (like valproate) can interfere with how the body uses folate [15].
  • Genetics: If a family has already had one child with a neural tube defect, the risk for future pregnancies is higher, and doctors typically recommend a much higher dose of folic acid (4.0 mg instead of the standard 0.4 mg) [17][18].

What to Expect Next

While the biological facts are important, they are only one part of your child’s story. Many children with spina bifida lead active, fulfilling lives. Your medical team will use tools like fetal MRI and ultrasound to pinpoint the exact location and type of the defect, which helps in creating a personalized care plan [19][20]. Identifying the “level” of the lesion—where it sits on the spine—is key, as lower lesions generally correlate with more physical mobility [21][22].

Common questions in this guide

What is the difference between open and closed spina bifida?
Open spina bifida occurs when the spinal canal is exposed to the outside environment, often with a visible sac. Closed spina bifida is covered by skin and may not be immediately obvious, sometimes only identified by a dimple, birthmark, or tuft of hair on the back.
What is the most severe type of spina bifida?
Myelomeningocele is the most common and severe form of open spina bifida. In this condition, a sac containing part of the spinal cord and nerves pushes through an opening in the back, which can cause nerve damage due to amniotic fluid exposure.
Does taking folic acid guarantee my baby won't have spina bifida?
While taking folic acid before and during early pregnancy significantly reduces the risk of neural tube defects, it does not prevent all cases. Spina bifida is caused by a complex mix of many different genetic and environmental factors.
What are the signs of spina bifida occulta?
Spina bifida occulta is often completely hidden and frequently causes no symptoms. In some cases, the only outward sign is a small tuft of hair, a dimple, or a birthmark on the lower back over the small gap in the spine.
How do doctors determine the severity of my baby's spina bifida?
Doctors typically use specialized imaging like fetal MRI and ultrasound to find the exact location and type of the spinal defect. Identifying the level of the lesion on the spine helps predict how it may affect your child's mobility, bladder, and bowel function.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Is my baby's spina bifida classified as 'open' (aperta) or 'closed' (occulta), and what does this mean for their prognosis?
  2. 2.At what level of the spine is the defect located, and how is that expected to affect my child's mobility and bladder/bowel function?
  3. 3.Are there signs of a Chiari II malformation or hydrocephalus on the imaging?
  4. 4.What are the benefits and risks of fetal (in-utero) surgery compared to surgery after birth for our specific case?
  5. 5.What specialists (e.g., neurosurgeons, urologists, orthopedists) should be part of our care team moving forward?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (22)
  1. 1

    Does India need 'mandatory flour fortification with folic acid' policy to prevent neural tube defects?

    Yadav V, Dabar D, Prasad P, et al.

    Journal of family medicine and primary care 2020; (9(7)):3787-3788 doi:10.4103/jfmpc.jfmpc_396_20.

    PMID: 33102376
  2. 2

    Single-cell transcriptomics reveals the cellular identity of a novel progenitor population crucial for murine neural tube closure.

    Deng Z, Carpinelli MR, Butt T, et al.

    Heliyon 2024; (10(17)):e37259 doi:10.1016/j.heliyon.2024.e37259.

    PMID: 39296075
  3. 3

    Spinal neural tube formation and tail development in human embryos.

    Santos C, Marshall AR, Murray A, et al.

    eLife 2024; (12()).

    PMID: 39636098
  4. 4

    Spinal Dysraphism in the Last Two Decades : What I Have Seen during the Era of Dynamic Advancement.

    Wang KC

    Journal of Korean Neurosurgical Society 2020; (63(3)):272-278 doi:10.3340/jkns.2020.0068.

    PMID: 32336058
  5. 5

    Brain malformations and cognitive performance in spina bifida.

    Schneider J, Mohr N, Aliatakis N, et al.

    Developmental medicine and child neurology 2021; (63(3)):295-302 doi:10.1111/dmcn.14717.

    PMID: 33140418
  6. 6

    Intracranial Translucency, Its Use as a Potential First Trimester Ultrasound Marker for Screening of Neural Tube Defects.

    Sepúlveda-González G, Arroyo-Lemarroy T, Basurto D, et al.

    Diagnostics (Basel, Switzerland) 2020; (10(11)) doi:10.3390/diagnostics10110986.

    PMID: 33266467
  7. 7

    Improved Bowel Function in Patients with Spina Bifida After Bone Marrow-Derived Mononuclear Cell Transplantation: A Report of 2 Cases.

    Liem NT, Chinh VD, Thinh NT, et al.

    The American journal of case reports 2018; (19()):1010-1018 doi:10.12659/AJCR.909801.

    PMID: 30143601
  8. 8

    Walking Function and Capacity in Middle-Aged and Older (59-66y) Adults With Spina Bifida Myelomeningocele: A 4-Year Follow-up Study.

    Klund-Hansen SL, Larsen KL, Lidal IB, et al.

    Archives of rehabilitation research and clinical translation 2025; (7(1)):100420 doi:10.1016/j.arrct.2024.100420.

    PMID: 40463775
  9. 9

    A rare case of thoracic lipomyelomeningocele in a young female: A case report.

    Sharma S, Khadka H, Aryal S

    Radiology case reports 2023; (18(3)):1372-1375 doi:10.1016/j.radcr.2022.10.042.

    PMID: 36819002
  10. 10

    Homologous cryopreserved amniotic membrane in the repair of myelomeningocele: preliminary experience.

    Marton E, Giordan E, Gioffrè G, et al.

    Acta neurochirurgica 2018; (160(8)):1625-1631 doi:10.1007/s00701-018-3577-x.

    PMID: 29858946
  11. 11

    The contribution of de novo coding mutations to meningomyelocele.

    Ha YJ, Nisal A, Tang I, et al.

    Nature 2025; (641(8062)):419-426 doi:10.1038/s41586-025-08676-x.

    PMID: 40140573
  12. 12

    Spina bifida as a multifactorial birth defect: Risk factors and genetic underpinnings.

    Wong ES, Hu DA, Zhang L, et al.

    Pediatric discovery 2025; (3(2)):e2517 doi:10.1002/pdi3.2517.

    PMID: 40666233
  13. 13

    Comparing Folic Acid Interventions and Arsenic Reduction Strategies for Neural Tube Defect Prevention in Bangladesh: A Systematic Review and Decision Analysis.

    Wei CF, Choma EF, Wang X, et al.

    Birth defects research 2025; (117(6)):e2494 doi:10.1002/bdr2.2494.

    PMID: 40552686
  14. 14

    Folic acid fortification of flour to prevent neural tube defects in Europe - A position statement by the European Board and college of obstetrics and gynaecology (EBCOG).

    Petch S, McAuliffe F, O'Reilly S, et al.

    European journal of obstetrics, gynecology, and reproductive biology 2022; (279()):109-111 doi:10.1016/j.ejogrb.2022.10.010.

    PMID: 36332537
  15. 15

    Association of maternal risk factors with the recent rise of neural tube defects in Canada.

    Liu S, Evans J, MacFarlane AJ, et al.

    Paediatric and perinatal epidemiology 2019; (33(2)):145-153 doi:10.1111/ppe.12543.

    PMID: 30920008
  16. 16

    Factors Associated With Neural Tube Defects Among Newborns Delivered at Debre Berhan Specialized Hospital, North Eastern Ethiopia, 2021. Case-Control Study.

    Mulu GB, Atinafu BT, Tarekegn FN, et al.

    Frontiers in pediatrics 2021; (9()):795637 doi:10.3389/fped.2021.795637.

    PMID: 35295317
  17. 17

    Pre-conception Folic Acid and Multivitamin Supplementation for the Primary and Secondary Prevention of Neural Tube Defects and Other Folic Acid-Sensitive Congenital Anomalies.

    Wilson RD, , Wilson RD, et al.

    Journal of obstetrics and gynaecology Canada : JOGC = Journal d'obstetrique et gynecologie du Canada : JOGC 2015; (37(6)):534-52 doi:10.1016/s1701-2163(15)30230-9.

    PMID: 26334606
  18. 18

    Mood-Stabilizing Anticonvulsants, Spina Bifida, and Folate Supplementation: Commentary.

    Patel N, Viguera AC, Baldessarini RJ

    Journal of clinical psychopharmacology 2018; (38(1)):7-10 doi:10.1097/JCP.0000000000000813.

    PMID: 29215383
  19. 19

    Fetal magnetic resonance imaging in the diagnosis of spinal cord neural tube defects: A prospective study.

    Gao G, Tao B, Chen Y, et al.

    Frontiers in neurology 2022; (13()):944666 doi:10.3389/fneur.2022.944666.

    PMID: 36003299
  20. 20

    Ultrasound and magnetic resonance imaging in the prenatal diagnosis of open spina bifida.

    Micu R, Chicea AL, Bratu DG, et al.

    Medical ultrasonography 2018; (20(2)):221-227 doi:10.11152/mu-1325.

    PMID: 29730690
  21. 21

    Spina Bifida: Pathogenesis, Mechanisms, and Genes in Mice and Humans.

    Mohd-Zin SW, Marwan AI, Abou Chaar MK, et al.

    Scientifica 2017; (2017()):5364827 doi:10.1155/2017/5364827.

    PMID: 28286691
  22. 22

    Multidisciplinary management of people with spina bifida across the lifespan.

    Koch VH, Lopes M, Furusawa E, et al.

    Pediatric nephrology (Berlin, Germany) 2024; (39(3)):681-697 doi:10.1007/s00467-023-06067-w.

    PMID: 37501019

This page explains the biology and types of spina bifida for educational purposes. Always consult your maternal-fetal medicine specialist or pediatric neurosurgeon regarding your child's specific diagnosis and care plan.

Get notified when new evidence is published on Spina bifida and other spinal dysraphisms.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.