Responses to mechanical and electrical stimuli are not attenuated by late pregnancy

Pregnancy has been associated with increased pain threshold. This study investigates the responses to mechanical and electrical stimuli in pregnant and non-pregnant women. Thirty pregnant women were subjected before and four days after elective caesarean section under regional anaesthesia to mechanical and electrical stimuli on both forearms. Thirty nonpregnant women were subjected to the same stimuli at the same time points. The responses to mechanical stimuli were expressed in mm of the Visual Analogue Scale (VAS) and averaged for both forearms. The VAS scores obtained after the electrical stimuli were divided by the mA recorded when the stimulus was applied, expressed in mm/mA and averaged. The responses to mechanical stimuli recorded before and four days after application did not differ between the two groups (F = 0.884, df = 3,116, P = 0.452). In the pregnant group the VAS values before and four days after the caesarean section were 16.4 +/- 14.4 mm and 12.8 +/- 12.5 mm respectively. In the nonpregnant group the VAS values recorded four days apart were 17.5 +/- 14.3 mm and 13.4 +/- 11.9 mm respectively. The responses to electrical stimuli applied four days apart also did not differ between the two groups (F = 2.433, df = 3,116, P = 0.069). The VAS values obtained after the first and second application of the electrical stimulus were 0.914 +/- 0.606 mm/mA versus 0.586 +/- 0.410 mm/mA in the pregnant and 0.853 +/- 0.538 mm/mA versus 0.725 +/- 0.467 mm/mA in the nonpregnant group. These results, under the study conditions, do not support the hypothesis that late pregnancy is associated with increased antinociception in humans.