Nonstress test:
The patient is studied in the semi-Fowler position, with monitoring of the fetal heart rate. A reactive pattern is defined as at least 2 episodes of fetal heart rate acceleration greater than 15 beats per minute lasting at least 15 seconds, associated with fetal movements, during a 30 minute study period. If less than 2 episodes are seen, then the pattern is termed nonreactive. If the fetus is nonreactive after 20 minutes, then the fetus is stimulated by either abdominal palpation or by administration of a glucose-containing drink.
Note: The nonstress test is to be distinguished from the contraction stress test, where fetal monitoring is done in the presence of uterine contractions occurring spontaneously, with nipple stimulation or after oxytocin infusion. In the nonstress test uterine contractions are not induced.
Amniotic fluid index:
The amniotic fluid index (see above) is calculated by measuring the diameter in centimeters of the largest amniotic fluid pocket in each of 4 quadrants overlying the gravid uterus, and then summing the total. Although values under 10 cm are low, the decision point is set to 5 cm.
Interpretation:
• If either the amniotic fluid index is <= 5 cm or the nonstress test is nonreactive, then a more complete evaluation is performed.
• If the amniotic fluid index is > 5 cm and the nonstress test is reactive, then continued monitoring is performed twice a week until delivery.
