nonstress

Nonstress is a term used in linguistics to describe syllables, words, or units of speech that do not bear primary or secondary stress in a given language. In stress-based phonology, some syllables are stressed while others are unstressed, or nonstressed. Unstressed vowels are often reduced in duration and openness, a phenomenon visible in many languages, including English, where unstressed vowels commonly become a schwa. The pattern of stressed and nonstressed syllables contributes to the rhythm and intonation of speech and can affect prosody and intelligibility without changing lexical meaning.

Nonstress test (NST) is a prenatal diagnostic procedure used to assess fetal well-being. It monitors fetal heart rate in response to fetal movement, typically using external sensors placed on the mother's abdomen. A reactive NST shows accelerations in the fetal heart rate, usually defined as two or more accelerations within a 20-minute period, with accelerations lasting a short duration and peaking above baseline; such a result suggests adequate oxygenation and nervous system responsiveness. A nonreactive NST lacks sufficient accelerations and may prompt additional testing, such as vibroacoustic stimulation, a contraction stress test, or a detailed ultrasound assessment. NST is commonly employed in pregnancies at higher risk (for example, maternal diabetes, hypertension, placental insufficiency) or when there is concern about reduced fetal movement. The test is noninvasive and provides information about fetal autonomic nervous system function.

Terminology and scope. The phrase nonstress may refer to both the linguistic concept of non-stressed syllables and the obstetric nonstress test; although unrelated, both terms describe a state where typical prominence signals are absent or not elicited. The usage depends on field and context.