The incidences of positive Kleihauer-Betke test in low-risk pregnancies and maternal trauma patients

Objective This study was undertaken to determine the incidence of positive Kleihauer-Betke (KB) tests in low-risk, third trimester patients and compare them with historical “control” patients who received KB tests for maternal trauma evaluations. Study design Institution Review Board approval was obtained. KB tests were performed on 100 low-risk gravid women at the time of their routine glucose challenge tests after informed consent. All specimens were analyzed for fetal hemoglobin using the Clayton modification. Patients with identified risk factors for placental abruption were excluded. A retrospective chart review was performed on 583 historical control patients from 1998 to 2001 who had undergone maternal trauma evaluations, of which 151 had a KB test at comparable gestations. Demographic data from medical records were reviewed and compared. Data were analyzed with 2-sided Student t test, Mann-Whitney rank sum, and χ2 tests, as indicated. Results Of the low-risk women 5 of 98 (5.1%) had a positive KB test, whereas 4 of 151 (2.6%) trauma patients had a positive test (P = .31). None of these positive results were associated with a clinical abruption or fetal distress. One low-risk patient with sickle cell trait had a 40 mL KB result. Conclusion The incidence of a positive KB test in low-risk pregnancies does not differ from maternal trauma patients. Therefore, the presence of a positive KB test alone does not necessarily indicate pathologic fetal-maternal hemorrhage in patients with trauma.