Pregnancy - How is Spina Bifida Detected?

If you are pregnant, you will be offered prenatal screening tests to check for spina bifida and other birth defects. These tests are not perfect. Even if the results are negative, there is still a small chance that spina bifida is present, and many mothers who have positive blood tests have normal babies. Speak with your doctor about prenatal testing, its risks and how you might handle the results. Prenatal testing is a personal choice.

Following are methods used to check for spina bifida during pregnancy:

• Blood tests. The primary test used to check for myelomeningocele is the maternal serum alpha-fetoprotein (MSAFP) test. In this procedure, your doctor draws a blood sample to be sent to a laboratory, where it's tested for alpha fetoprotein (AFP), a protein that's produced by the fetus. It's normal for a small amount of AFP to cross the placenta and enter the mother's bloodstream, but abnormally high levels of AFP may indicate that the fetus has a neural tube defect. Varying levels of AFP can be caused by factors including a miscalculation in fetal age or multiple fetuses. If this occurs, your doctor may order a follow-up blood test for confirmation. If the results are still high, you will need further evaluation, including an ultrasound examination.
• Ultrasound. Many obstetricians use ultrasonography to screen for spina bifida. If blood tests indicate high AFP levels, your doctor will suggest an ultrasound exam to determine why. Ultrasound exams bounce high-frequency sound waves off tissues in your body to form black and white images on a small video monitor. The information these images provide can help establish whether there is more than one fetus and can help confirm gestational age - factors that can alter AFP levels. An advanced ultrasound can also detect signs of spina bifida, such as an open spine or particular features in your baby's brain that may indicate spina bifida. Ultrasound today is quite effective in detecting spina bifida and assessing its severity. This procedure is safe for both mother and baby.
• Amniocentesis. If a blood test shows high levels of AFP in your blood and the ultrasound is normal, your doctor may offer an amniocentesis. During an amniocentesis, your doctor uses a needle to remove samples of fluid from the amniotic sac that surrounds the fetus. The analysis indicates the level of AFP present in the amniotic fluid. A small amount of AFP is normally found in amniotic fluid, however the amniotic fluid contains an elevated amount of AFP when an open neural tube defect is present because the skin surrounding the baby's spine is gone and AFP leaks into the amniotic sac. A second test can be done on the same sample to confirm that a neural tube defect is present. However, an amniocentesis cannot indicate the severity of spina bifida. This test does have a risk to the developing fetus - about one in 200 to one in 500 pregnant women miscarries after an amniocentesis.
  

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