Spectral analysis of fetal heart rate variability might offer additional information that can be used for assessing the fetal condition more reliably. Clinical recordings of fetal heart rate are usually contaminated by artifacts. These artifacts can be detected and corrected or removed, but this can affect the spectral estimates obtained from the heart rate data. To determine what level of artifact correction is still acceptable for reliable calculation of spectral heart rate variability parameters, artifact correction is simulated on neonatal and fetal data that did originally not contain artifacts. 2000 data segments with various levels of artifact correction are analyzed spectrally, and calculated spectral estimates are compared to the values obtained from the original, artifact free data. In the very low ( 0.04 Hz) and low (0.04 - 0.15 Hz) frequency range, powers can be calculated reliably when up to 25% of the data are missing due to artifact correction. Powers in the high frequency range (0.15 - 0.4 Hz for adults, 0.4 - 1.5 Hz for newborns) cannot be calculated reliably when data are missing due to artifact correction. This is a major limitation for application in clinical practice, which might be solved by calculating power in the high frequency range at a shorter time scale than power in the low frequency range. Short segments of heart rate data that are free of artifacts can then be used to calculate powers in the high frequency range reliably, while segments that contain artifacts are excluded.