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: 32–33 gestational weeks (GW), 39–40 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 32–33 GW (median ± IQR: 39.6 ± 0.7 °C), at 39–40 GW (40.6 ± 1.1 °C) and at early stage of active labour (40.8 ± 1.5 °C) as compared to 20 non‐pregnant controls (p