Variation in the depth of the epidural space in successive pregnancies

The epidural records of 151 patients who had received two effective lumbar epidurals during subsequent labours were studied. For each patient the depth of the epidural space from the skin was recorded at both insertions and the differences between the two measurements compared. Factors which are known to cause a variation in this value were excluded. The skin to epidural space depth was virtually unchanged in 72 (47.7%) of the repeat epidurals. In 18 cases (11.9%) however, the measured depth of the epidural space differed by more than 1.5 cm from one insertion to the next. Possible explanations for these differences are discussed.