How do Labour Positions Alter Pelvic Outlet Dimensions?

In the second stage of labour, flexible-sacrum and upright positions for women without epidural analgesia, and side-lying positions for women with epidural analgesia, reduce the likelihood of instrumental birth. It is unclear, however, if these outcomes may be related to changes in pelvic outlet dimensions. A comprehensive literature review was performed to collate the evidence on the effect of labour positions on outlet dimensions. Four articles were included in the review, and it was found that kneeling squat and hands and knees positions may create larger pelvic outlet dimensions than supine or semilithotomy positions.