Non-invasive fetal electrocardiogram (FECG) through multichannel maternal abdominal sensing requires a suitable signal processing in order to enhance the signal-to-noise ratio and produce a single FECG signal from which parameters of interest, such as fetal heart rate (FHR), can be determined. Several processing techniques have been presented in the literature, which can benefit from the number of channels involved in the processing. Among these, the recently presented spatio-temporal filtering (STF) performs a weighted sum of QRS complexes to produce the enhanced FECG signal, whose weighting coefficients are calculated on the basis of the quality of synchronization among different channels. After analyzing clinical FECG signals and proving that a deterministic time offset can affect abdominal FECG channels, the paper proposes an algorithm for the automatic compensation of such systematic effect, as a pre-processing block of STF-like techniques.