Abnormal baseline variability in fetus is defined as:

Normal baseline variability is more than 5 and less than 25 .It is measured by estimating the difference in beats per minute between the highest peak and lowest trough of fluctuation in a one minute segment of the trace.5 bpm or less is considered reduced variability. Refer page no 529,520,521 of Text book of obstetrics,sheila balakrishnan,2 nd edition. Absence of accelerations, reduced base line variability of < 5 bpm for > 90 minutes denote a hypoxic fetus. Decreased baseline variability may be due to fetal sleep, infection, hypoxia, anomalies or due to maternal medications. Reduced baseline variability, with late or variable deceleration increases the risk of CP. Interpretation of the CTG should always be made in the context of clinical picture. Reference: Dutta's Textbook of Obstetrics 7th edition page no 611