The Influence of Maternal Height, Obstetrical Conjugate and Fetal Birth‐weight in the Management of Patients with Breech Presentation
Authors: Mahmood Tahir A. 
Published: February 2008

EDITORIAL COMMENT: This paper should interest readers since it analyses a series of 424 breech presentations in mature pregnancies (fetal malformations excluded) in which the Caesarean section rate was 55% and the perinatal mortality rate nil in the 311 patients having a trial of labour. All patients had erect lateral X‐ray pelvimetry and the variables considered were maternal height and pelvic size, and fetal birth‐weight, in terms of outcome of trial of labour.

The author found that maternal height over 166 cm was not associated with an anteroposterior diameter of the pelvic inlet of <11 cm (0 of 56), whereas in women shorter than 154 cm the incidence was 21 % (22 of 106) — this finding is not of much use in decision making since 11 cm is not a criterion of pelvic contraction (see later). The summary of the paper implies that ultrasonographic plus clinical assessment of fetal size allows judgement of when trial of vaginal delivery is appropriate management of a patient with persistent breech presentation (failed or contraindicated external cephalic version), and a lesser degree of pelvic contraction. It is suggested that ‘small or average‐sized breech babies can deliver through a small pelvis’— How small the pelvis? How small the baby? We believe that with the inaccuracy inherent in assessment of fetal size, an attempt to exercise clinical judgement in these circumstances is not justified by the data in this paper.

It is true that women with contracted pelves can sometimes deliver average‐sized babies safely by vaginal breech delivery — this does not prove that the decision to allow them to do so was prudent. We agree with the author that X‐ray pelvimetry is a prerequisite before embarking upon trial of vaginal delivery in breech presentation; indeed X‐ray pelvimetry is one of the few remaining indications for X‐ray examination of the pregnant patient.

Opinions are divided as to whether or not there is ever a place for trial of labour in breech presentation. The trial of labour finesse was devised for trial of the pelvic brim in vertex presentations. Unfortunately a patient with a contracted pelvis and a less than average‐sized baby presenting by the breech can labour well and deliver within a few hours with the infant dying because of tentorial tears (see Case 2, table 4, Beischer N A Pelvic contraction in breech presentation, J Obstet Gynaecol Brit Cwlth 1966, 73: 421–427).

It should be noted that in Dr Mahmood's paper only erect lateral X‐ray pelvimetry was performed so that the transverse diameters of the pelvis were not considered. In our opinion vaginal breech delivery of a term infant is contraindicated when there is significant contraction of the pelvis according to the following criteria:Brim

Anteroposterior diameter 10.0 cm or less

Transverse diameter 12.0 cm or less

Mid‐pelvis

Interspinous diameter 9.0 cm or less

Interspinous plus posterior segment 13.5 cm or less

Outlet

Available anteroposterior diameter 9.5 cm or less

Intertube'rous diameter 9.5 cm or less

Interspinous plus available anteroposterior diameter 20.0 cm or less

Summary: The value of erect lateral X‐ray pelvimetry for selecting patients for a safe trial of vaginal delivery was assessed in a retrospective study of 424 women with a breech presentation. A trial labour was more often allowed in women with larger inlet conjugate measurements and the chance of successful vaginal delivery was better with larger pelvic measurements. However, there was no absolute level of pelvic contraction below which vaginal delivery was impossible. The size of the fetus did not determine the rate of planned elective Caesarean section. A fetus weighing greater than 3,500 g, had less than 50% chance of vaginal delivery. It is suggested that antenatal assessment of fetal size should be considered in patients with breech presentation before deciding on the mode of delivery.