Spina Bifida Association
What is Spina Bifida?
Spina Bifida describes a group of neural tube defects (NTD's) that occur when the baby's developing spine (neural tube) fails to close properly. When most people speak of SB, they are referring to the most common and also most severe form, called myelomeningocele, which causes the spinal nerves to bulge through an opening in the back.
What causes SB?
There is no single known cause for SB. It is due to a complex interaction of both genetic and environmental factors occurring very early in the pregnancy (by the 4th week). The genetic factors that can cause SB are not well known. Research has shown that supplementation of folic acid (a "B" vitamin) reduces the risk of having a pregnancy affected by SB. However, many people who take folic acid still have babies with SB, and women who did not take folic acid still have healthy babies. No one knows why. It just happens. This means that there is still much to learn about the causes of SB, and it is nobody's fault.
How is SB diagnosed during pregnancy?
- Maternal Serum Alpha: Fetoprotein (MSAFP): Also known as triple test or quad test, MSAFP is a blood test performed between the 15th and 20th weeks of pregnancy to determine if there is a higher risk for NTD. MSAFP testing measures the level of a protein (AFP) made by the fetus and placenta. Small amounts of this protein normally cross the placenta into the maternal bloodstream, but when very high levels cross, it could be that the fetus has an NTD. However, MSAFP testing is not used as a diagnostic tool but rather as an indicator that further testing is needed, because the test is not specific for SB, and because high MSAFP may be present for a number of other reasons.
- Ultrasound: is the primary diagnostic tool for prenatal diagnosis of SB and other NTD's. It is a non-invasive technique that produces an image of the fetus. It can be used to identify many different problems in fetuses, but can also be used to identify important characteristic signs of SB in both the brain and spine. Cranial markers include the lemon sign (abnormal shape of fetal skull), the banana sign (crowding of the cerebellum in the back part of the head), and hydrocephalus (abnormally large ventricles or fluid spaces in the brain). The normal fetal spine resembles a string of pearls. An SB spine will appear as a string of pearls with some broken or missing pieces.
- Fetal MRI: May be recommended after the diagnosis is made through ultrasound to determine severity of SB. MRI is a powerful technology that uses magnetic imaging (not radiation) to give better pictures of the fetal spinal cord and spinal nerves. Through MRI, the doctors can see the size and extent of the SB. This information helps them explain the diagnosis and prognosis (expected long term condition) in greater detail. Fetal MRI is not necessary for all pregnancies affected by SB though, particularly when the ultrasound images are good.