Antepartum fetal heart rate testing: I. Evolution of the nonstress test

Abstract

On May 1, 1975, at Women's Hospital, Los Angeles County-University of Southern California Medical Center, a new antepartum fetal heart rate (AFHRT) protocol was put into clinical use. This included the widely used contraction stress test (CST) and a new concept of nonstress testing (NST). The NST was based on FHR response associated with fetal movements and was categorized as reactive (normal) or nonreactive (abnormal). The nonreactive fetus was then evaluated with a CST if not contraindicated. During the 24 months, May 1, 1975 to April 30, 1977, a total of 2,422 NST's were done in 1,169 patients, with 1,547 (64 per cent) reactive and 829 (35 per cent) nonreactive. CST was done 939 times, with 851 (90.6 per cent) negative, 29 (3 per cent) positive, 13 (1.4 per cent) equivocal, and 46 (5.0 per cent) unsatisfactory. There were ten (3.3 per cent) perinatal deaths within one week of a negative CST, five (1.0 per cent) within one week of a reactive NST, and two (8.7 per cent) with a positive CST. A reactive NST was as predictive of good outcome as was a negative CST. Analysis of the nonreactive NST showed that two or more accelerations were not associated with abnormal CST's. Also, some nonreactive fetuses became reactive with oxytocin and had good outcome. These observations were utilized in the development of a newer, shorter NST which allows for fetal stimulation in an attempt to further define fetal well-being.