Baseline: a computer method of calculating baseline in fetal heart rate recordings

'Baseline' estimation is of fundamental importance in both visual and numerical analysis of fetal heart rate recordings, even though the baseline itself is in reality an imaginary line. Here we describe a linear method of estimating baseline in fetal heart rate recordings. The method is easy to implement on a digital computer, and is capable of precise mathematical analysis. Non-linear methods, on the other hand, introduce unpredictable and non-quantifiable statistical bias, and are best avoided.