Maternal posture in second stage and fetal acid base status

The effect of position during the second stage on outcome was studied in 58 women, with no exclusions because of pregnancy complications or signs of fetal distress, who were randomly allocated to have the second stage conducted in either the dorsal or 15 degrees lateral tilt position. All the women were of parity 0 or 1 and the two groups were well matched except for gestational age at delivery. There were no differences in clinical outcome between the two groups, but overall the dorsal group had lower cord artery pH values (P less than 0.05), higher PCO2 (P less than 0.01) and a greater base deficit, but not significantly so. pH and base deficit were similar in both groups where the second stage did not last greater than 15 min. Thereafter, there was a trend to decreasing pH and increasing base deficit with increasing length of second stage in the dorsal group, but not in the tilt group though this did not reach statistical significance. Low Apgar scores, complicated pregnancy and first pregnancy were each associated with significantly lower pH levels. Prolonged placement of the patient in the flat dorsal position should be avoided in second stage, though a suitable alternative under the conditions described has not been defined.