Which foetal pelvic variables are useful for predicting right-rotational or left-rotational birth?

Objective: To assess the variables useful to predict right-rotational birth (ROA) and left-rotational birth (LOA), through the analysis of a large number of foetalpelvic variables, using discriminant analysis. Materials and methods:One hundred and two pregnant women were included in this single centre prospective study.For each mother-foetus pair, 43 pelvic and 18 foetal variables were measured.Partial least squares-discriminant analysis was performed to identify foetal-pelvic variables that could statistically separate the 3 delivery modality groups: non-rotational birth or occiput anterior (OA), right-rotational birth and left-rotational birth.Results: For the OA versus LOA model, the most efficient variable for discrimination was the inlet-mid-plane angle.For the OA versus ROA model, the most important variable was the sacral overhang.For both model, we found that women with small foetuses, anthropoïd inlet, reduce posterior space of the mid-plane and reduce oulet were more likely to have non-rotational birth.Conclusion: This analysis helps us in identifying foetal-pelvic conditions to the rotation in physiological cases.It should be relevant to perform a similar work with cases of posterior position during explusion stage.