About the Authors

Nozomi Donoyama

Roles Conceptualization, Data curation, Funding acquisition, Investigation, Methodology, Project administration, Writing – original draft

donoyama@k.tsukuba-tech.ac.jp

Affiliation Department of Health, Faculty of Health Sciences, Tsukuba University of Technology, Tsukuba, Ibaraki, Japan

Toyomi Satoh

Roles Conceptualization, Methodology, Resources, Supervision

Affiliation Department of Obstetrics and Gynecology, University of Tsukuba, Tsukuba, Ibaraki, Japan

Tetsutaro Hamano

Roles Data curation, Formal analysis, Methodology, Supervision, Visualization, Writing – original draft

Affiliation P4 Statistics Co. Ltd., Setagaya-ku, Tokyo, Japan

Norio Ohkoshi

Roles Funding acquisition, Supervision, Visualization

Affiliation Department of Health, Faculty of Health Sciences, Tsukuba University of Technology, Tsukuba, Ibaraki, Japan

Mamiko Onuki

Roles Resources

Affiliation Department of Obstetrics and Gynecology, University of Tsukuba, Tsukuba, Ibaraki, Japan

Competing Interests

One of the authors (TH) runs a commercial company P4 Statistics Co. Ltd., Tokyo, Japan. However, this does not alter our adherence to PLOS ONE policies on sharing data and materials. All other authors have no competing interests to declare.