Objective: The pain threshold in humans rises during late pregnancy, and the woman becomes less sensitive to stress. The aim of this study was to investigate whether monitoring the sympathetic nervous system response to stimuli by skin conductance activity might be a useful predictor of spontaneous onset of labour in post-term pregnancies.
Study design: A prospective observational study. Fifty-two healthy pregnant women were consecutively asked for inclusion in the study at their post-term pregnancy examination. Initially, a Ctg (cardiotocography) registration was performed, followed by 5 min of skin conductance measurement including a "cold pressor test". Finally, a vaginal examination with a cervical assessment were performed according to clinical guidelines.
Results: A statistically significant lower pain reaction during the period of provocation was seen in deliveries close to spontaneous onset of labour compared with induced deliveries with an non-spontaneous onset of labour before 294 days (p = 0.02). Sixty-three per cent (19/30) of the women with spontaneous onset had a negative value at provocation compared with 30% (6/20) in the induced group.
Conclusions: Decreased response to pain stimuli, as an indication of decreased activity in the sympathetic nervous system, has a correlation to spontaneous onset of labour in post-term pregnancies.
Keywords: Pain stimuli; skin conductance; spontaneous onset of labour; sympathetic activity.