Background:  Cardiotocographic (CTG) recordings of the fetal heart remain standard obstetric practice among hypertensive women. Changes in the short‐term variation (STV) in the fetal heart are often attributed to the effect of anti‐hypertensive medications, regardless of the fact that this principle has never been validated.
Aim:  To assess the STV of CTG recordings pre‐ and post‐ the anti‐hypertensive medication, clonidine.
Methods:  Forty hypertensive pregnant women, already receiving the anti‐hypertensive clonidine, were recruited. The CTGs were conducted pre‐ and post‐dose administration. The CTGs were assessed by the Sonicaid Team® automated CTG analysis (Oxford Instruments, UK) to avoid CTG assessor bias. Baseline fetal heart rate (FHR) (delta change from pre‐ and post‐dose) and STV were compared using spss v.14® utilising Student t‐tests.
Results:  No statistical difference was found in the pre‐ and post‐baseline FHRs (P = 0.48). The mean delta baseline heart rate before and after drug administration was −0.54 bpm. The STV of the CTGs recorded pre‐ and post‐clonidine dose was also not affected by administration of the drug (P = 0.34). The mean delta STV before and after drug administration was 0.39 ms. Two women received betamethasone 12 mg intramuscularly within the 12‐h period prior to CTG recordings to enhance fetal lung maturity. The mean STV for the fetuses of these women pre‐drug was 4.8 ms and 13.2 ms post‐administration. This was the largest delta seen in all STVs recorded in this dataset.
Conclusion:  The anti‐hypertensive drug clonidine does not alter baseline FHRs or affect the STV of the FHR in hypertensive pregnant women.