Footnotes

• Contributors KF: design of study; acquisition, analysis and interpretation of data; and drafting and revisions of the manuscript. SR: conception and design of study, analysis and interpretation of data and revisions of the manuscript. PGD: conception and design of study, analysis and interpretation of data, and revisions of the manuscript. BOJ: conception and design of study, analysis and interpretation of data, and revisions of the manuscript. DH: conception and design of study, analysis and interpretation of data and revisions of the manuscript. RWH: conception and design of study, analysis and interpretation of data, and revisions of the manuscript. BJM: conception and design of study, analysis and interpretation of data, and revisions of the manuscript. All authors approved the submission of the manuscript for consideration of publication and agreed to be accountable for all aspects of the work.

• Competing interests None declared.

• Patient consent for publication Not required.

• Ethics approval Ethical approval was granted by the Human Research Ethics Committee at The Royal Women’s Hospital, and also at the surgical unit, The Royal Children’s Hospital, Melbourne (HREC 36246A).

• Provenance and peer review Not commissioned; externally peer reviewed.