Relationship of nonstress test reactivity and gestational age.

The relationship between gestational age and reactivity during the nonstress test was evaluated in 297 high-risk patients. When the incidence of nonreactive tests at gestational ages of 28 to 44 weeks was evaluated week-by-week, either on the basis of tests performed or patients tested, there was no statistically significant relationship between reactivity and gestational age (P = .184 tests; P = .222 patients). Four grouped gestational-age intervals were evaluated. Interval A consisted of the period from 28 to 32 weeks' gestation, interval B consisted of the period from 33 to 36 weeks' gestation, interval C consisted of the period from 37 to 41 weeks' gestation, and interval D consisted of the period from 42 to 44 weeks' gestation. The incidences of nonreactive tests were 15.3, 3.9, 2.5, and 5.9% in intervals A, B, C, and D, respectively. The differences in the incidences of nonreactive tests between those performed in intervals A and B and intervals A and C were highly statistically significant (P less than .001). Differences in the incidences between other intervals did not reach statistical significance. The incidences of patients who experienced a nonreactive test were 10.2, 2.4, 2.8, and 4.7% in intervals A, B, C, and D, respectively. The differences in the incidences of patients who experienced a nonreactive test in intervals A and B and intervals A and C were highly statistically significant (P less than .001). Differences in the incidences between other intervals did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)