Computerised antenatal fetal heart rate recordings between 24 and 28 weeksof gestation

Objective To assess computerised fetal heart rate recordings between 24 and 28 weeks of gestation for gestation related differences. Design Prospective, cross sectional observational study. Setting Liverpool Women's Hospital. Population 112 women 28 at 27 weeks, 30 at 26 weeks, 27 at 25 weeks and 27 at 24 weeks of gestation, respectively. Methods Fetal heart recordings of 60 minutes duration were performed once i n each pregnancy using the System 8000 fetal heart rate programme (System 8 000, Oxford Sonicaid Ltd, Chichester, UK). For each gestational age, record s were analysed for short term variation, basal heart rate, accelerations a nd time spent in high episodes. Results The mean short term variation increased with gestation (P = 0.05). No record had a short term variation <4 msecs. There was no relationship be tween heart rate and increasing gestation. The mean number of accelerations per record increased with increasing gestation (P < 0.01). 20% of recordin gs showed no accelerations > 15 bpm. The mean duration spent in episodes of high variation increased with gestation (P = 0.05) 13% of recordings showe d no time spent in high episodes. All fetuses had normal outcomes at delive ry. Conclusions Absence of episodes of high variation or absence of acceleratio ns is not an abnormal finding at lower gestations. The standard threshold o f 4 msecs for short term variation appears to remain valid at lower gestati ons. These differences should be considered when using computerised CTG ana lysis at early gestations.