Study concept and design: Smith, Nelson, Lawlor.
Acquisition, analysis, or interpretation of data: Smith, Tilling, Nelson, Lawlor.
Drafting of the manuscript: Smith, Lawlor.
Critical revision of the manuscript for important intellectual content: Tilling, Nelson.
Statistical analysis: Smith.
Obtained funding: Nelson, Lawlor.
Study supervision: Tilling, Nelson, Lawlor.
Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Nelson reported having participated in advisory boards for and received speakers’ fees from Beckman Coulter, Besins, Ferring, Merck Serono, Merck Sharp & Dohme, and Roche Diagnostic. No other disclosures were reported.
Funding/Support: Drs Smith, Tilling, and Lawlor work in a unit that receives funding from the UK Medical Research Council (http://www.mrc.ac.uk) (MC_UU_12013/5 and MC_UU_12013/9), and Dr Lawlor receives support from a National Institute for Health Research Senior Investigator award (NF-SI-0611-10196). This work is also supported by a grant from the Wellcome Trust (http://www.wellcome.ac.uk), which pays Dr Smith’s’ salary (WT094311MA).
Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review or approval of the manuscript; and decision to submit the manuscript for publication.
Disclaimer: All views are those of the authors and not necessarily those of the Human Fertilisation and Embryology Authority (HFEA).
Additional Contributions: We thank the staff of the HFEA and the contributing UK clinics for these data.