Pregnancy‐induced analgesia: a combined psychophysical and neurophysiological study

Background To investigate changes in heat pain threshold and modifications in heat pain processing during pregnancy and labour, seventy-six nulliparous pregnant women were enrolled in two studies. Methods In the first study (psychophysical), 60 pregnant women underwent a quantitative sensory testing (QST) investigating heat perception in two body areas (right forearm and T10 dermatome) according to these groups: 3233 gestational weeks (GW), 3940 GW, early stage of active labour and 24?h after the delivery. In the other study (neurophysiological), contact heat-evoked potentials (CHEPs) were recorded in other 16 women at the 32nd GW and in 11 of these also at the 40th GW. Results The psychophysical study showed that heat pain threshold was significantly increased at the forearm at 3233 GW (median +/- IQR: 39.6 +/--0.7 degrees C), at 3940 GW (40.6 +/- 1.1 degrees C) and at early stage of active labour (40.8 +/- 1.5 degrees C) as compared to 20 non-pregnant controls (p?