A nonstress test is a screening test used in pregnancy

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

. A cardiotocograph

Cardiotocography

In medicine , cardiotocography is a technical means of recording the fetal heartbeat and the uterine contractions during pregnancy, typically in the third trimester...

 is used to monitor the fetal

Fetus

A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

 heart rate.

Premise

The premise of the NST is that a well-oxygenated, non-acidemic fetus

Fetus

A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

 will spontaneously have temporary increases in the fetal heart rate (FHR).

Interpretation

• Reactive (normal)- presence of two or more fetal heart rate accelerations within a 20-minute period, with or without fetal movement discernible by the woman.
• Nonreactive- presence of less than two fetal heart rate accelerations within a 20-minute period over a 40-minute testing period.

Vibroacoustic stimulation

Vibroacoustic stimulation

Vibroacoustic stimulation is the application of a vibratory sound stimulus to the abdomen of a pregnant woman to induce FHR accelerations. The presence of FHR accelerations reliably predicts the absence of fetal metabolic acidemia. Vibroacoustic stimulation is typically used during a nonstress...

can wake the fetus, and is sometimes used to speed up the test or to facilitate further evaluation of a nonreactive nonstress test.