1. Prenatal Blood Tests
During the second trimester of pregnancy, women have the opportunity to have a blood test to screen for birth defects. This is called the maternal serum triple or quadruple screen. This test only involves drawing blood from the mother and does not pose any risk for the fetus. The maternal serum triple or quadruple screen tests for a number of abnormalities including neural tube defects like spina bifida. Elevated levels of alpha-fetoprotein (AFP) in the blood can indicate a neural tube defect because this substance can leak from an open spinal canal in the fetus into the mother's blood stream. This test alone, however, is not enough to diagnose spina bifida, as false positives are not uncommon.
2. Prenatal Ultrasound Tests
Ultrasound tests are a common part of prenatal care. In some cases, a severe spinal abnormality may be detected in a fetus prior to the maternal serum triple or quadruple screen. More commonly, however, a positive blood test will indicate the need for an ultrasound to investigate further. High levels of AFP may also indicate multiple fetuses or a later gestational age than previously believed, both of which can be determined by ultrasound. While a fetal ultrasound can strongly suggest severe spina bifida, it cannot rule out mild spina bifida. Some mild cases of spina bifida may not cause enough of a spinal abnormality to be detected by ultrasonography.
3. Amniocentesis Tests
Amniocentesis tests are done by extracting amniotic fluid from the sac that surrounds the fetus. The fluid is then tested for AFP and an enzyme called acetylcholinesterase (ACH). An amniocentesis is usually done to confirm the findings of a blood test and ultrasound. If levels of AFP and ACH are elevated and an ultrasound shows spinal abnormalities, spina bifida is strongly suspected. Amniocentesis tests do pose a risk for a fetus, however. Between 1 in 200 and 1 in 500 pregnancies miscarry following this test. Parents must weigh the risks of the test with the advantage an early diagnosis brings.
