Heart rate variability (HRV) has been recognised as a non-invasive method for assessing cardiac autonomic regulation. Aiming to characterize HRV changes at labour in women, we studied 10 minute ECG recordings from young mothers (n=30) at the third trimester of pregnancy (P) or during augmentation of labour (L) (n=30). Data of the L group were collected when no-contractions (L-NC) or the contractile activity (L-C) was manifested. Accordingly, the inter-beat interval (IBI) time series were processed to estimate relevant parameters of HRV such as the mean IBI (IBI ), the mean heart rate HR , the root mean square of successive differences (RMSSD) in IBIs, the natural logarithm of high-frequency component (LnHF), the short-term scaling parameters from detrended fluctuation and magnitude and sign analyses such as (alpha1, alpha1(MAG), alpha1(SIGN)), and the sample entropy (SampEn). We found statistical differences (p<0.05) for RMSSD among P and L-NC/L-C groups (25 +/- 13 vs. 36 +/- 14/34 +/- 16 ms) and for LnHF between P and L-NC (5.37 +/- 1.15 vs. 6.05 +/- 0.86 ms(2)). Likewise, we identified statistical differences (p<0.05) for alpha1(SIGN) among P and L-NC/L-C groups (0.19 +/- 0.20 vs. 0.32 +/- 0.17/0.39 +/- 0.13). By contrast, L-NC and L-C groups showed statistical differences (p<0.05) in alpha1(MAG) (0.67 +/- 0.12 vs. 0.79 +/- 0.12), and SampEn (1.62 +/- 0.26 vs. 1.20 +/- 0.44). These results suggest that during labour, despite preserving a concomitant non-linear influence, the maternal short-term cardiac autonomic regulation becomes weakly anticorrelated (as indicated by alpha1(SIGN)); furthermore, an increased vagally mediated activity is observed (as indicated by RMSSD and LnHF), which may reflect a cholinergic pathway activation owing to the use of oxytocin or the anti-inflammatory cholinergic response triggered during labour.