Is X-ray pelvimetry useful in a trial of labour after caesarean section?

In a trial of labour after caesarean section, X-ray pelvimetry has generally been regarded as an important part in the evaluation of patients before a decision is made. A review of 445 patients with trial of labour has shown that although the measurements of the pelvic inlet were greater in patients who delivered vaginally, the incidence of successful trial was not related to the measurements of the pelvis. Maternal height was also unrelated to the outcome. Only a history of previous vaginal delivery was predictive of a successful trial. The results suggest that X-ray pelvimetry is not necessary in the majority of patients if the past obstetric history and the clinical assessment are in favour of a successful trial. It is only useful when there is doubt and in this case both a lateral and an antero-posterior film are necessary as the obstetric conjugate alone was unreliable in predicting the transverse diameter of the inlet as well as the outcome.