[Long-memory of labor pain]

The aim of the study was to investigate the stability of labour pain recall 14-21 months after delivery, and to relate it to events during labour.

One hundred and fifteen primipara completed a visual analogue scale (VAS) on the second day after delivery, and a similar VAS 14-21 months later. Women who were delivered before completing 37 gestational weeks, had a multiple pregnancy, needed epidural analgesia, or whose infant was transferred to the neonatal care unit were excluded. Data were analysed by three different methods to minimise bias. By method 1, the proportion of VAS 2 > VAS 1 was calculated. By method 2, the accuracy of recall was defined from the equation -1 < or = VAS 2--VAS 1 < or = 1. By method 3, the VAS used was regarded as an unlimited scale, but with all observations shortened to the interval, 0 to 10 cm. Pain scores were related to obstetrical data: instrument delivery, fetal weight, duration of second stage of labour, use of pethidine and use of pudendal analgesia.

Thirteen of 20 women (65%) who had received pethidine during labour reported a higher VAS 2 than VAS 1, compared to 27 of 95 (28%) women who had not received pethidine (p = 0.003). According to method 2, 35% of the pethidine-treated women overestimated labour pain on recall, compared to 13% in the non-pethidine-treated group (p < 0.05). According to method 3, women who were not treated with pethidine showed a decrease of 0.81 cm on the recalled VAS, compared to an increase of 1.13 cm in the pethidine-treated group (p < 0.01). None of the other investigated events during labour were related to pain recall.

In general, labour pain recall fades over time or tends to be stable, but to a significantly higher number of women receiving pethidine, pain seems to intensify on recall. If further investigations show that this is an effect of pethidine itself, opioids should be used with caution during labour.