Neural tube defects are usually diagnosed before the infant is born, through laboratory or imaging tests.

Prenatal laboratory tests include:
"Triple screen" blood test: One part of the triple screen blood test is a test for an elevated level of alpha-fetoprotein (AFP), which is associated with a higher risk of neural tube defects. The AFP test also can be done by itself. The two other parts of the "triple screen" involve testing for human chorionic gonadotropin (hCG) and estriol. This test generally is done during the second trimester.

Amniotic fluid tests: Testing of amniotic fluid may also show a high level of AFP, as well as high levels of acetylcholinesterase; health care providers might conduct this test to confirm high levels of AFP seen in the triple screen blood test. The amniotic fluid also can be tested for chromosomal abnormalities, which might be the cause of the abnormal AFP level. Prenatal ultrasound imaging usually detects almost all types of neural tube defects.

When an infant with a diagnosed or suspected neural tube defect is born, the health care provider will perform tests to assess its severity and complications. These tests might include X-ray, magnetic resonance imaging, computed tomography scan to look for spinal defects or excess fluid, and measuring the head circumference; assessing the infant’s vigor, motor, and sensory functioning; and observing the infant’s urinary stream.