The nonreactive nonstress test: predictive value for neonatal anemia in the isoimmunized pregnancy

Abstract

Objective: To assess the value of the fetal nonstress test (NST) in predicting neonatal transfusion in pregnancies complicated by red cell isoimmunization.

Methods: We retrospectively reviewed the records of all patients evaluated for isoimmunization in pregnancy for the period January 1992 to December 1994. In addition to prenatal care, serial ultrasonography, and invasive testing when indicated, patients had NSTs two times per week. Nonstress tests were interpreted as either reactive or nonreactive using standard criteria. Results of the last NST before delivery were analyzed. Neonatal outcome data were obtained prospectively and by chart review.

Results: Sixty patients with isoimmunization were identified during the study period. Fifty-one patients (85%) had reactive NSTs until delivery, and nine (15%) had nonreactive NSTs that prompted delivery. Twelve of 51 (23.5%) patients with reactive NSTs and seven of nine (77.8%) patients with nonreactive NSTs required neonatal transfusion (P = .003, odds ratio 11.4 [95% confidence interval (CI) 1.7-120.2]). The mean (standard error of the mean; range) hematocrit (%) at birth was 38.9 (3.0; 21.3-52.0) in patients with reactive NSTs and 28.3 (3.8; 14.5-45.0) in those with nonreactive NSTs (P < .05). A nonreactive NST had a 77.8% positive predictive value (95% CI 49.0-100) in identifying the need for neonatal transfusion.

Conclusion: These findings indicate that a nonreactive NST is predictive of subsequent neonatal transfusion in patients with isoimmunization. The antepartum fetal NST is a useful adjunct in the management of isoimmunized pregnancies.