N–P

neural tube defects BIRTH DEFECTSin which the
neural tube, the precursor to the SPINAL CORDand
BRAIN, fails to develop properly. The neural tube
develops in the first few weeks of gestational life
and may be complete by the time a woman knows
she is pregnant. An open neural tube defect
exposes the brain and spinal cord outside the
body. SKINand spinal structure abnormally encase
a closed neural tube defect, typically involving
only the spine (and usually the lower spine).
Though there are associations between neural
tube defects and CHROMOSOMAL DISORDERSsuch as
DOWN SYNDROME, most researchers believe neural
tube defects occur as a combination of random
GENE MUTATIONand environmental circumstances.
The most serious neural tube defect is anen-
cephaly, in which the brain does not form. Anen-
cephaly is always fatal. SPINA BIFIDA, in which the
spinal column does not close properly, can result
in mild to debilitating deformity and disability. The
mildest form of spina bifida is myelomeningocele,
in which the defect affects only a small portion of
the lower spinal cord. Reconstructive surgery can
improve protection of the spinal cord, though a
degree of PARALYSISaffecting bowel, BLADDER, and
lower body function typically remains. Occasion-
ally a neural tube defect is so minor that it does
not become apparent until later in life, even adult-
hood.
Folic acid supplementation, ideally beginning
before CONCEPTION, can prevent most neural tube
defects. Health experts recommend all sexually
active women of childbearing age take folic acid
supplements whether or not they plan PREGNANCY.
(Folic acid supplementation also helps stabilize
blood glucose levels in pregnant women who have
DIABETES.) ALPHA FETOPROTEIN(AFP), CHORIONIC VILLI
SAMPLING(CVS), and prenatalULTRASOUNDcan detect

most neural tube defects before birth, allowing

women and their doctors to make decisions about

the course of the pregnancy and care needs fol-

lowing birth. Doctors often recommend terminat-

ing the pregnancy when the neural tube defect is

so severe that death of the infant would be certain

and immediate after birth.

See also ABORTION; CONGENITAL ANOMALY; KYPHO-

SIS; SCOLIOSIS.

occupational health and safety Work-related

injuries account for about 6,000 deaths and 16

million health-care visits each year in the United

States. There are literally thousands of hazards in

the workplace, some common to nearly all jobs

and others unique to specific occupations. In the

United States, the Department of Labor, the Occu-

pational and Health Safety Agency (OSHA), the

Centers for Disease Control and Prevention

(CDC), and the National Institute for Occupational

Safety and Health (NIOSH) oversee workplace

safety regulations, standards, and procedures.

OSHA further has enforcement authority for com-

pliance issues. Other federal and state organiza-

tions also participate in workplace safety.

MOST COMMON CAUSES OF

WORKPLACE FATALITIES IN THE UNITED STATES

drowning ELECTROCUTION

falls from roofs and ladders fires and explosions

MOTOR VEHICLE ACCIDENTS overturned equipment

struck by falling objects substance exposure

suicide VIOLENCE

Employers are responsible for providing a

working environment free from unreasonable risk

to workers. Such an environment varies according

to occupation. To the extent possible, federal and

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