NST (Non Stress Test) in pregnancy

The non stress test ( NST ) monitors the fetal heart rate in response to
the fetal well being. It has advantage of involving no external stimulation
( eg.- oxitocin stimulating ) in the conduct of test.

Indication -
i) Maternal -
   -  Post dated pregnancy.
   -  Rh sensitization.
   -  Maternal age 35 or more.
   -  Chronic renal disease.
   -  Hypertension.
   -  Sickle cell disease.
   -  Diabetes.
   -  Premature rupture of membrane.
   -  History of still birth.
   -  Trauma.
   -  Vaginal bleeding in 2nd and 3rd trimester.

ii) Fetal -
    -  Decreased fetal movement.
    -  Intrauterine growth retardation (IUGR).
    -  Oligohydramnios / polyhydramnios.
    -  Fetal evaluation after amniocentesis.


Preparation and Positioning - 
The woman bladder should be empty and provide semi-fawler's and left 
lateral position. Her blood pressure (BP) should be checked to obtainted
a baseline recording.


Procedure - 
                    NST is based on pattern of fetal heart rate reactivity to fetal
movement. Normally the fetal heart rate decreased and variable increased
with gestation age, probably in relation to the development of the central nervous
system (CNS).
                        The fetus normally has a transient accelerated heart rate with
average baseline variability when moving or to external stimuli such as abdominal
palpation. And abnormal fetal heart rate reactivity/response to fetal movement is
evident by a persistent reduction in baseline variability with an absence of fetal
heart rate acceleration. This pattern may indicates a distressed fetus and occurs
when the fetal CNS is depressed by drugs, hypoxia or acidosis.
                                     A reactive test is one in which a normal fetal reactivity is
demonstrate this is evidenced by fetal heart rate acceleration of 15 beat/min above
the baseline lasting for 15 to 30 sec in association with fetal movements two or
more occurrence of this acceleration pattern within a 10 min period of 5 or more
acceleration within a 20 min period are considered normal. A normal fetus near
term will also evidenced a baseline fetal heart rate between 120 to 160 beats/min
and no declaration any time. A non-reactive test is one in which there is a persistent
decreased variability with an absence of acceleration in fetal heart rate in response
to fetal movement. This is evidence by fetal heart rate acceleration or less than
15 beat/min above the baseline or lasting less than 15 sec in association with fetal
movements.
                    A reactive test indicates fetal well being and predicts a good outcome
if birth will to occur within one week.
                    If the test is non reactive further assessment of fetal status should be
initiated to aid in obtaining fetal well being.