The lambda fetal heart rate pattern: an assessment of its significance in the intrapartum period

The "lambda" fetal heart rate (FHR) pattern was first described in 1977 as a pattern involving an acceleration followed immediately by a deceleration. However, its clinical significance has not been elucidated. During 6 months, 56 patients with this pattern were identified, representing 4% of all deliveries during this period. These were compared with a control group of 500 consecutive low-risk term patients who had been monitored electronically. The lambda pattern generally appeared early in labor and lasted for a variable period of time, but rarely persisted throughout labor. The relative rates of low Apgar scores, cesarean sections, and associated nonreassuring FHR patterns were similar between the two groups. The timing or depth of the decelerative portion of the pattern did not appear to correlate with any adverse outcome. Therefore, it does not appear that the lambda pattern is associated with any adverse outcome, nor does it predict the development of other concerning FHR patterns.