HINT: Spina bifida and
anencephaly are neural tube defects, and among the most common preventable birth defects,
and result in different degrees of damage to the spinal cord and nervous system. NTDs (neural tube defects) are birth defects that occur very early in pregnancy.
The defects develop between the 17th and 30th day after conception (four to six
weeks after the first day of a woman's last menstrual period), usually before a
woman knows she is pregnant. During this critical time of pregnancy, the proper
formation and closure of the neural tube, which later becomes the spinal cord,
brain, and bone surrounding the spinal cord and brain, normally takes place. A
neural tube defect occurs when the neural tube fails to close properly.
Anencephaly and spina bifida are the two most common NTDs. Anencephaly is a
fatal condition in which the upper end of the neural tube fails to close. In
these cases, the brain fails to develop completely or is entirely absent.
Pregnancies affected by anencephaly often result in miscarriages, and the
infants who are born alive die very soon after birth. Spina bifida occurs when
the lower end of the neural tube fails to close. As a result, the spinal cord
and back bones do not develop properly. Sometimes a sac of fluid protrudes
through an opening in the back, and often a portion of the spinal cord is
contained in this sac. Paralysis of the infant's legs, loss of bowel and bladder
control, hydrocephalus ("water on the brain"), and learning disabilities are
often associated with spina bifida. Eighty to 90% of infants born with spina
bifida survive. Despite varying degrees of disability, many lead long,
successful, and productive lives.