Fetal heart rate changes observed on the CTG trace during instrumental vaginal delivery.

INTRODUCTION: Instrumental vaginal delivery (IVD) helps expedite delivery during second stage of labour so as to avoid a second stage caesarean section. However, due to mechanical effects on the fetal head, vacuum and forceps may cause cardiotocograph (CTG) abnormalities due to vigal stimulation as well as increased intracranial pressure.

OBJECTIVE: To determine the features observed on the CTG during IVD in term pregnancy and correlate them to perinatal outcomes.

METHODS: A retrospective analysis of 445 cases who had vacuum deliveries (227) and forceps deliveries (218) at St. George's University Hospitals NHS Foundation Trust during a 12-month period was performed. CTG features were analysed at 10 minutes prior to and immediately after applications of the chosen instrument till delivery. Specific abnormalities were correlated to Apgar score and umbilical blood pH.

RESULTS: Specific CTG abnormalities after applications of vacuum and forceps were: tachycardia (99 (43.61%) versus 88 (40.37%)), increased baseline fetal heart rate (FHR) [14 (6.17%) versus 4 (1.83%) p = .0204], baro-receptor-mediated "variable" deceleration (101 (44.49%) versus 85 (38.99%)), chemoreceptor-mediated "late" deceleration (62 (27.31%) versus 76 (34.86%)), prolonged deceleration (32 (14.10%) versus 24 (11.01%)), saltatory pattern [35 (15.42%) versus 76 (34.86%) p < .0001], and reduced baseline variability (10 (4.41%) versus 7 (3.21%)). There were no significant differences in the mean Apgar Scores at 1 and 5 minutes between ventouse and forceps delivery (8 and 9, respectively) or the umbilical blood pH (both >7.20).

CONCLUSIONS: After application of instruments, 90% of CTG traces showed abnormal features. Tachycardia, baro- and chemoreceptor-mediated decelerations, and saltatory patterns were the most common abnormalities. Increased baseline FHR during vacuum as compared to forceps delivery was possibly secondary to pain/pressure and resultant sympathetic overactivity. The saltatory pattern was more common in forceps deliveries, possibly secondary to increased intracranial pressure and resultant autonomic instability. Despite these CTG abnormalities, the perinatal outcomes were good.