In vitro myometrial contractility reflects indication for caesarean section S Quenby, a A Matthew, b J Zhang, b F Dawood, c S Wray b a Clinical Sciences Research Institute, University of Warwick, Coventry b Translational Research Institute, University of Liverpool, Liverpool c Liverpool Women’s NHS Foundation Trust, Liverpool, UK Correspondence: Dr S Quenby, Warwick Medical School, Clinical Sciences Research Institute, Clifford Bridge Road, Coventry CV2 2DX, UK. Email: s.quenby@warwick.ac.uk Accepted 10 April 2011. Published Online 27 July 2011. Objective To assess the extent to which in vitro measurements of myometrial contractility reflect the clinical indication for caesarean section. Design A prospective, observational hypothesis-generating study. Setting Women were recruited from Liverpool Women’s NHS Foundation Trust and experiments were performed in the Physiology Department at the University of Liverpool. Population Myometrial samples were taken from women undergoing a caesarean section during labour (n = 50) or from women having a repeat nonlabouring caesarean section (n = 70). Methods The demographic characteristics of the women and indications for current and previous caesarean sections were recorded. The force, frequency and duration of spontaneous contractions of myometrial strips, and changes in the intracellular calcium concentration of the strips, were measured. Kruskall– Wallis and post hoc tests were used to assess the significance of differences between groups. Results Samples from women whose caesarean section was for fetal distress/acidosis (scalp pH <7.2) contracted with more force than those from women whose caesarean section was for delay in the first stage of labour (P < 0.001). For repeat, nonlabouring caesarean sections, samples from women whose first caesarean section was for fetal distress/acidosis also contracted with more force than did samples from women whose first caesarean section was for delay in the first stage of labour (P = 0.03). Conclusions These findings suggest that the myometrium contracts with greater force in women who have a caesarean section for fetal distress. Keywords Calcium signalling, fetal distress, myometrial contractility. Please cite this paper as: Quenby S, Matthew A, Zhang J, Dawood F, Wray S. In vitro myometrial contractility reflects indication for caesarean section. BJOG 2011;118:1499–1506. Introduction The contribution of myometrial contractility to pathologi- cal labour is poorly understood because it is difficult to assess. Standard tocography only records the frequency and duration of uterine contractions, and not force generation. Intrauterine pressure catheters can be used to assess uterine muscle force generation. However, the value of information obtained using these catheters is diluted by the inherent variability of pressure recordings and must be weighed against the risks of insertion, which include infection, cord entanglement and uterine perforation. 1,2 Some authors argue that the benefits of using pressure catheters outweigh these infrequent but significant risks. 3 If in vitro contractility mirrored in vivo contractility, then this would allow further research into the myometrial contribution to pathological labours. In this hypothesis-generating study, we initially investigated whether in vitro myometrial contractility altered with the onset of labour. Next, we compared parameters of in vitro contractility in women having nonlabouring and labouring caesarean sections. We then investigated whether inter-patient variability in parameters of in vitro contractility could be accounted for by differences in the clinical indication for caesarean section. Finally, we investigated whether in vitro myometrial contractility in women having a repeat caesarean section in a subsequent pregnancy was influenced by the indication for the first caesarean section. If the myometrium has an intrinsic propensity for excessive or reduced contractility, this would have important scientific and clinical conse- quences. ª 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2011 RCOG 1499 DOI: 10.1111/j.1471-0528.2011.03064.x www.bjog.org Basic science