Fetal behaviour in uncomplicated pregnancies after 41 weeks of gestation

The development of fetal behaviour and of fetal behavioural states (FBS) has been well defined in preterm and term fetuses. However, FBS have not yet been studied after term, although this is a potentially very dangerous period and clinical management is controversial. We investigated fetal behaviour in normal pregnancies after 41 weeks of gestation (287 days, menstrual age, GA) as compared to control term fetuses. Furthermore, we wanted to see if the findings might have consequences for clinical management. Twelve healthy women with GA between 289 and 298 days participated. All pregnancies were reliably dated and at the time of the study, there was a normal amount of fluid. Twelve healthy women with GA 273-287 days served as controls. All subjects underwent a behavioural study using cardiotocography to record the heart rate (CTG), and two ultrasound scanners to observe body and eye movements, as described previously. All fetuses in both groups clearly exhibited FBS 1F-4F which fitted the definitions of Nijhuis et al. The median percentage of FBS 3F and 4F ('awake states') increased significantly from 6% in the term group to 21.5% in the fetuses after 41 weeks (P = 0.014). FBS 1F ('quiet sleep') and 2F ('active sleep') decreased from 92 to 78% (P = 0.014), mainly at the expense of FBS 2F which decreased from 78 to 58% (P = 0.002). This indicates increasing wakefulness in utero. The fetal heart rate patterns (FHRP) associated with FBS 3F and 4F were impressive. For example, in FBS 4F, the FHRP showed large amplitude, prolonged accelerations which fused into a sustained tachycardia with only short periods of return to the baseline, resembling tachycardia with decelerations. We conclude that in normal pregnancies after 41 weeks, the development of the fetal central nervous system continues, resulting in an increasing percentage of 'fetal wakefulness'. The CTG-patterns that result from these behaviours can easily mimic fetal distress and one should be aware of this phenomenon. Whether behavioural studies can be used to distinguish 'normal' from 'abnormal' fetuses after term awaits further study.