How is Spina Bifida Diagnosed?

In most cases, spina bifida is diagnosed before the baby is born. However, some mild cases may go unnoticed until after birth. Very mild cases, in which there are no symptoms, may never be detected.

Prenatal (Before Birth) Diagnosis

Various screening tests to check for spina bifida and other birth defects have become a routine part of prenatal care. However, these tests are not without flaws; some may miss the presence of a neural tube defect and others may indicate one that turns out to be nothing.

Blood tests

The major test that doctors rely on to detect spina bifida is the maternal serum alpha-fetoprotein (MSAFP) test. During your second trimester, your doctor will take a sample of your blood and send it to a laboratory, where it will be tested for alpha fetoprotein (AFP). This is a specific protein that the developing fetus produces. If the test reveals abnormally high levels of AFP, it may suggest that the fetus has a neural tube defect – such as spina bifida. But not all cases of spina bifida result in high AFP levels. By the same token, not all high AFP levels mean that the fetus has a neural tube defect. Other explanations include a pregnancy with multiple fetuses and an error in estimating fetal age. A repeat test may be ordered to make sure that the test result is not a mistake. The AFP test generally detects about 80 percent of babies with spina bifida.

In addition to the MSAFP test, several other blood tests may be useful. These include tests to look for the following substances:

  • Human chorionic gonadotropin (HCG), a hormone produced in the placenta
  • Estriol, an estrogen produced by both the fetus and the placenta
  • Inhibin A, another hormone produced in the placenta

The use of all four of these tests may be referred to as a quadruple screen. If only three tests are performed, it is called a triple screen. These screens also may help detect the presence of other birth defects such as a chromosomal abnormality.

Ultrasound

If the blood test shows high levels of AFP, your doctor will probably recommend an ultrasound examination to help find out the cause. With ultrasound technology, high-frequency sound waves bounce off tissues in the body to create images on a video monitor. These images can tell if there are multiple fetuses inside the uterus. They also can help establish the age of the fetus. A more advanced form of ultrasound examination can visualize indications of spina bifida – like an open spine. Ultrasound is an effective tool for prenatal diagnosis of spina bifida and is safe for both mother and baby.

Amniocentesis

If a blood test reveals high levels of AFP and the ultrasound is normal, your doctor may suggest that you undergo an amniocentesis. With this procedure, a needle is introduced into the amniotic sac and a sample of fluid is removed for analysis. If a high AFP level is found, this points to an open neural tube defect because the protein has leaked out of the spine and into the amniotic sac. Amniocentesis does present some risk, leading to miscarriage in between one in 200 and one in 500 pregnancies.

Postnatal (After Birth) Diagnosis

With two forms of spina bifida – meningocele and myelomeningocele – diagnosis after birth is obvious. Milder cases of spina bifida that are not diagnosed during prenatal testing may be detected after the child is born. Milder forms may be diagnosed do to an abnormality of the skin or structure of the back (e.g. a hairy, dark or vascular birth mark over the lower spine or a deep pit over the spine above the gluteal cleft). Sometimes a mild form of spina bifida is diagnosed when an X-ray of the lower spine is taken for another reason. Sometimes medical issues such as difficulty control the bowels or bladder or abnormal tone in the legs may lead to the diagnosis of a mild form of spina bifida. If spina bifida is suspected, doctors may use ultrasound (in early infancy), magnetic resonance imaging (MRI) or a computed tomography (CT) scan to get a clearer view of the spine and vertebrae. If hydrocephalus (excess fluid in the brain) is suspected, the doctor may request a CT scan and/or X-ray of the skull.

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Resources:

Mayo Clinic
Tests and Diagnsosis