The prevalence, aetiology and clinical significance of pseudo-sinusoidal fetal heart rate patterns in labour.

OBJECTIVE: To investigate the prevalence of sinusoidal and pseudo-sinusoidal fetal heart rate (FHR) patterns in labour and the relation between the characteristics of the FHR pattern and fetal outcome. DESIGN: A prospective observational study over a 6-month period in which all women who had continuous FHR monitoring in labour had their intrapartum cardiotocographs (CTGs) scrutinized for the presence of sinusoidal or pseudo-sinusoidal FHR patterns. SETTING: John Radcliffe Hospital, Oxford. SUBJECTS: 1520 women who had fetal monitoring during labour for various reasons. MAIN OUTCOME MEASURES: Both internal (electrocardiographic) and external (ultrasound) recordings of the FHR were analysed. Abnormal FHR patterns were related to obstetric characteristics and fetal outcome in terms of Apgar scores, umbilical artery pH and admission to the special care unit. RESULTS: No true sinusoidal FHR patterns were observed, but pseudo-sinusoidal FHR patterns were found in 230 of the 1520 CTGs examined (15%). Of these, 219 were classified as minor (amplitude 5-15 beats/min) and 11 as intermediate (amplitude 16-24 beats/min). Major pseudo-sinusoidal FHR patterns (amplitude greater than 24 beats/min) were not observed. Minor pseudo-sinusoidal FHR patterns had a mean duration of 21 (SD 13) min and typically occurred once or twice early in labour. Using logistic regression analysis a significant, independent relation was demonstrated between the presence of minor pseudo-sinusoidal FHR patterns and the use of pethidine (RR 1.84, 95% CI 1.3 to 2.59, P less than 0.0001) and epidural analgesia (RR 1.85, 95% CI 1.24 to 2.76, P less than 0.001). Intermediate pseudo-sinusoidal FHR patterns were found in association with both in utero fetal sucking and transient episodes of fetal hypoxia such as that caused by periodic umbilical cord compression. CONCLUSION: Pseudo-sinusoidal FHR patterns in labour will usually be associated with a normal fetal outcome but a careful fetal assessment is mandatory.