BACKGROUND: We evaluated whether baseline maternal heart rate variability (HRV), including the Analgesia Nociception Index (ANI), is associated with maternal hypotension and fetal heart rate (FHR) abnormalities following combined spinal-epidural (CSE) labor analgesia. METHODS: Laboring women were enrolled in this prospective observational study. The primary endpoint was maternal hypotension. The secondary endpoint was FHR abnormalities within 30鈥痬in following CSE analgesia initiated with intrathecal plain bupivacaine 1.0鈥痬g and fentanyl 20鈥痬icrog. The maternal ANI, electrocardiogram, blood pressure, heart rate, oxygen saturation, and FHR tracings were recorded 15鈥痬in before and 30鈥痬in after CSE. Parturients were grouped based on presence of hypotension and FHR abnormalities. Patient demographics and HRV metrics were compared. Receiver operating characteristics (ROC) curves were constructed for the prediction of hypotension and FHR abnormalities. RESULTS: No significant intergroup differences were detected in patient characteristics. Several baseline HRV metrics and ANI differed significantly between the normotensive (n鈥?鈥?0) and hypotensive (n鈥?鈥?1) groups and between parturients showing FHR abnormalities (n鈥?鈥?9) and those showing reassuring FHR traces (n鈥?鈥?2). The area under the ROC curve (AUC) for predicting hypotension of the baseline low-frequency (LF)/high-frequency (HF) ratio was 0.677 (95% CI 0.55 to 0.80), and that of the ANI was 0.858 (95% CI 0.78 to 0.94). For predicting non-reassuring FHR patterns, the AUC of the LF/HF ratio was 0.77 (95% CI 0.65 to 0.89), and that of the ANI was 0.833 (95% CI 0.72 to 0.94). CONCLUSIONS: The ANI can predict the propensity for maternal hypotension and non-reassuring FHR patterns following CSE.