Neural tube defects (spinal dysraphisms)
Birth defects or abnormalities that occur in the development of the spinal cord and brain of some babies are called Neural tube defects (NTDs). During the first month of intrauterine life, an embryo (developing baby) grows a primitive tissue structure called the ‘neural tube’. As the embryo develops, the neural tube begins to change into a more complicated structure of bones, tissue and nerves that will eventually form the spine and nervous system. If the seam of the neural tube does not close correctly, portions of the spine, the covering of the spinal cord (meninges) or the cord itself can push outside of the back as the fetus grows resulting in NTDs.
Types of NTDs
There are two types of NTDs. The most common type are called the open NTDs. Open NTDs occur when the brain and/or spinal cord are exposed at birth through a defect in the skull or vertebrae (back bones). Examples of open NTDs are spina bifida (myelomeningocele), anencephaly, and encephalocele. Rarer types of NTDs are called closed NTDs. Closed NTDs occur when the spinal defect is covered by skin. Common examples of closed NTDs are lipomyelomeningocele, lipomeningocele, and tethered cord.
If baby has spina bifida, the tiny bones of the spine don’t close completely, and part of the spinal cord pokes through the spine. Anencephaly is caused when the upper part of the neural tube that forms the brain doesn’t close completely.
Symptoms of NTDs
The symptoms associated with NTDs vary depending on the specific type of defect. Symptoms include physical problems (such as paralysis and urinary and bowel control problems), blindness, deafness, intellectual disability, lack of consciousness, and, in some cases, death. For example children with spina bifida may have paralysed legs (not able to move) and bladder- bowel incontinence. Babies with anencephaly condition are missing major parts of the brain, skull and scalp. They do not survive long after birth, usually for just a few hours.
Causes and risks of NTDs
Neural tube defects are considered a complex disorder because they are caused by a combination of multiple genes and multiple environmental factors like certain drugs, cigarette smoke, air pollution and lead may be harmful for pregnancy. Risk factors for NTDs are- family history, previous history of baby with NTDs, anti seizure drugs, obesity, diabetes, opioids intake during first two months of pregnancy etc.
Intrauterine diagnosis of NTDs
There are prenatal screening tests to find out risk of NTDs in fetus. These include-
1) Maternal blood screening (quad screening)- done between 15 to 22 weeks of pregnancy.
2) Ultrasound- done at 16 to 20 weeks of pregnancy.
3) Amniocentesis- done at 15 to 20 weeks of pregnancy.
Prevention
All women of childbearing age should eat a diet high in folic acid or take a multivitamin with 400 micrograms of folic acid each day, especially one month prior to conception through the first three months of pregnancy. Adequate folate levels are critical during the early days of the developing embryo, particularly the 3rd and 4th week, the period in which neural tube defects occur and when many women won't know they are pregnant.
Video by Dr Shivraj Singh
content by Dr Mukta Meel