Population differences affect nonstress test reactivity.

Abstract

The nonstress test (NST) is the most widely used test of fetal well-being. Recently it has been suggested that race may play a role in NST reactivity. The objective of this research was to explore population variables in addition to race that may influence NST reactivity. Study subjects were 1263 black and 658 white women who underwent NST in the week preceding delivery at a tertiary facility. Retrospective analysis of data from a comprehensive database was conducted. It was found that the percentage of black women with a nonreactive NST was more than three times the percentage of white women, and that from 35 weeks' to 42 weeks' gestation there were significantly fewer reactive NSTs for blacks than for whites (P less than .05). Racial differences in NST results persisted in a logistic regression analysis controlling for several population variables including pregnancy complications and demographic and behavioral factors (odds ratio 3.81; 95% CI 3.03 to 4.78). Regression analysis also confirmed that gestational age, maternal education, epilepsy, and smoking significantly influenced NST reactivity. These results indicate that population differences in NST reactivity exist at our facility. Further prospective study of population determinants of NST reactivity is needed to determine how race, test indication, and other clinical, demographic, and behavioral variables should be used in interpretation of tests of fetal well-being. Standard criteria for NST testing may not be useful in all obstetrical populations.